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NSSH Part 647
Soil Map Development
Definition and Purpose (647.00)
Soil map development includes activities related to the preparation and completion of maps for soil
survey. The purpose is to provide current and accurate soil maps (digital and analog) and related
products to users. Four functional areas describe the major cartographic procedures: imagery acquisition,
map compilation, digital data capture, and map finishing.
- Imagery Acquisition
Field mapping in soil survey relies on
aerial photography as base imagery. Publications and SSURGO development use orthophotography where
it is available. Generally about two years before the start of the soil survey, the memorandum of
understanding initiates the acquisition of imagery for mapping and publication.
Part 647.02 explains
acquisition of imagery.
- Map Compilation
Map compilation is the accurate transfer of map information from soil
survey field sheet imagery to publication imagery or map bases for digitizing, and the accurate
conversion or correlation of soil map unit symbols and features to approved legends.
Standard compilation techniques encourage precise transfer of information from soil survey field
sheets to approved map bases for digitizing and map finishing.
- Digital Data Capture
Digital data capture or digitizing is the process of converting information
shown on analog maps into digital form for computer processing. Mapping on hard copy aerial photography,
subsequently compiling to orthophotography, and hand- or scan- digitizing are avoided if at all possible. Field
mapping is done using electronic media and on-screen digitizing as much as possible to avoid these extra steps.
This part establishes digital standards and specifications for the digital soil survey map component
of the Soil Survey Geographic (SSURGO) database.
- Map Finishing
Map finishing is the final transfer of line work and text to a product ready
for press negatives.
Policy and Responsibilities (647.01)
- Policy
- The publication scale for new and updated soil surveys is 1:12,000 or 1:24,000. Alaska
for 1:25,000 and the Caribbean for 1:20,000 are excepted.) Other scales require approval
by the Director, Soil Survey Division, of the Natural Resources Conservation Service.
- All new and updated soil surveys are to be digitized and SSURGO certified.
- The publication format for a map is 3.75 minute or 7.5 minute quadrangle. Soil maps for
publication of new and updated soil surveys rely on digital map finishing. This process captures
all correlated map features in the publication in a digital format.
- An approved and signed memorandum of understanding for the soil survey area must be on file
at the NRCS National Soil Survey Center, Lincoln, Nebraska, and the NRCS National Cartography
and Geospatial Center, Fort Worth, Texas, before processing a request to order imagery.
Part
606.01(a)(5) and Exhibits 606-1 and
606-2 provide additional information on the memorandum of
understanding.
- Soil surveys use the definitions and applications of soil survey features on NRCS-SOI-37A
in Exhibit 627-5. Definitions of ad hoc features are the responsibility of the MLRA regional
office.
- Responsibilities
- The Federal Geographic Data Committee and the Office of Management and Budget
formally assigned the responsibility for national coordination of digital soil data to the NRCS.
Refer to Office of Management and Budget Circular A-16, for more information.
- The Natural Resources Conservation Service (NRCS) has the Federal responsibility
for the National Cooperative Soil Survey and Federal leadership for:
- collecting, storing, maintaining, and distributing soil information on privately owned
lands in the United States. These activities include
- preparing compilation bases for digitizing and map finishing
- performing the quality assurance of soil survey maps, and
- preparing map materials for publication.
- NRCS also has the lead Federal responsibility in collecting, archiving, and distributing
the Soil Survey Geographic (SSURGO) database.
- The MLRA soil survey office is responsible for:
- achieving an exact or acceptable join as described in the NSSH 609.03 and specified in
the memorandum of understanding,
- supervising map compilation (or coordinate with dedicated map compilation units if
established) in preparation for digitizing and publication as described in NSSH part 647,
- quality control of map compilation activities (100% check),
- quality control of all phases (soil business) of soil surveys,
- initiating documentation on discrepancies of joins, and
- the total scientific quality, including accuracy, completeness, and logic, of all soil
survey maps in the soil survey area.
Part 609.05 provides additional information.
- The MLRA regional office is responsible for:
- assuring all aspects of active soil survey projects,
- assuring that exact or acceptable joins are achieved as specified in the memorandum
of understanding,
- performing correlation activities in a manner that will lead to a seamless coordinated
soil survey throughout MLRAs and between MLRAs,
- assuring the definitions of ad hoc features,
- approving all correlation documents, including amendments to previously correlated surveys,
in coordination with the appropriate state conservationist,
- assuring the quality of all map compilation/recompilation/digitizing through a 10% check
and certification (a locally administered certification process may be established where
dedicated compilation units exist),
- informing states of any deficiencies in work submitted for review. Assisting states with
the resolution of these problems,
- assuring the quality of soil databases and tables,
- assisting states in the preparation of metadata,
- coordinating with states as needed for delivery of all map materials, soil data, and metadata
to the digitizing unit for processing,
- coordinating and providing quality assurance for products of map digitizing and finishing,
- coordinating the certification letter with digitizing units and appropriate state
conservationists,
- initiating plans for completing an exact join between soil surveys that do not have an
exact join.
- The state office is responsible for:
- obtaining all map materials needed in the state to perform map compilation/recompilation
activities, including those needed for a check of joins with other survey areas,
- coordinating with MLRA soil survey offices in the state concerning the flow of map compilation
work,
- determining priorities for soil survey areas to be digitized within each state,
- identifying and working with organizations outside of NRCS that can help us achieve our
digitizing goals and coordinating with digitizing units, digital map finishing sites, and MLRA
regional offices concerning these activities,
- deploying sufficient staff to achieve agreed upon goals for the digitizing initiative,
- reviewing joins with surrounding surveys and making corrections in coordination with the
MLRA regional office to achieve an exact join for recompilation of existing surveys,
- supervising recompilation (or coordinating with dedicated map compilation units if established),
- quality control of map recompilation activities (100% check),
- initiating correlation amendments/supplements through the MLRA regional office as needed
for recompiled soil surveys,
- preparing and providing metadata for all compiled/recompiled surveys from the state which are
submitted to digitizing units (through the MLRA regional office) for digitizing,
- certifying and downloading soil tabular data for SSURGO for all compiled/recompiled surveys
from the state which are submitted to digitizing units (through the MLRA regional office) for
digitizing,
- after passing digitizing quality control and quality assurance checks: certifiying SSURGO and
archiving to the Soil Data Warehouse,.
- archiving certified SSURGO to the Soil Data Warehouse, at which time it is automatically publicly
distributed via the Soil Data Mart, Web Soil Survey, and Geospatial Data Gateway.
- In-house distribution of SSURGO among NRCS field offices,
- providing to a digital map finishing site all layers for publication in digital format compatible
with digital map finishing processes.
- Digitizing units are responsible for:
- coordinating compilation/recompilation and soil business activities with states and MLRA
regional offices to ensure an orderly flow of work for all soil surveys which are to be digitized
by the unit,
- performing certification review of submitted materials,
- notifying MLRA regional offices of any problems discovered during certification review which
require action by the MLRA regional office or states prior to certification,
- digitally capturing compiled map materials including scanning soil lines, labeling, edge
matching, and digitizing linear and point features,
- performing quality control of final digital data including spatial (100 % hardcopy check
plot review by producing mylar check plots), tabular, and metadata,
- coordinating with the MLRA regional office to obtain a SSURGO (Exhibit 647-5) letter from
the state conservationist of the state whose survey is digitized, and
- exporting the spatial data to the staging server
- Digital map finishing sites are responsible for:
- electronically preparing soil survey maps for negative preparation by the National Cartographic
and Geospatial Center,
- coordinating soil business activities with states and MLRA regional offices to ensure and
orderly flow of work for all soil surveys which are to be map finished at the site, and
- >performing quality control with 100 percent edit.
- The National Cartography and Geospatial Center is responsible for:
- providing training in SSURGO quality assurance activities,
- providing technical assistance to states, MLRA regional offices, and digitizing units in
spatial, tabular and metadata development to meet SSURGO specifications,
- assisting digitizing units with error
resolutions to successfully import spatial data to
staging server,
- assisting states with resolving problems related
to committing SSURGO datasets to the Soil Data
Warehouse,
- communicating changes/updates and enhancements
to SSURGO standards, certification routines and
procedures,
- performing 10% quality review of SSURGO
materials (spatial layer and metadata) documenting
SSURGO spatial and tabular discrepancies, and
forwarding findings to digitizing units, MO office,
and other digital capture entities,
- developing and updating map compilation and
digitizing techniques and standards,
- coordinating and implementing software updates
to reflect changes in standards,
- providing digital map finishing processes,
procedures, and training to offices conducting
digital map finishing,
- archiving, distributing certified SSURGO and
Digital General Soil Map data (Gateway and
Electronic Media),
- developing and maintaining SSURGO and other
geospatial standards, protocols, specifications and
training,
- migrating new data set boundaries into the Soil
Data Warehouse,
- updating SSURGO status map on the Soil Data
Mart,
- developing and providing Digital Map Finishing
processes, standards, protocols, specifications and
training,
- performing 10% quality assurance review of
digital map finishing materials,
- coordinating and implementing geospatial
software updates to reflect changes in standards and
specifications.
- The National Soil Survey Center is responsible for:
- developing standards, guidelines, and procedures for all aspects of soil survey work, soil
map development, and SSURGO certification,
- developing and applying geographic information systems for use with soil survey activities;
and
- developing, maintaining, and improving soil survey geographic databases.
- providing technical assistance in population of the NASIS database.
- The Soil Survey Division is responsible for:
- reviewing and monitoring the SSURGO development process,
- issuing policy,
- coordinating with states, MLRA regional offices, National Cartography and Geospatial Center,
and National Soil Survey Center on soil survey compilation, digitizing, and map finishing
issues.
Imagery (647.02)
- Initiation of Imagery Acquisition
Acquisition of imagery for mapping and publication of soil surveys begins about
2 years before fieldwork is to begin. It starts with a memorandum of understanding (MOU) between the Natural
Resources Conservation Service and the State and local governments, universities, or other cooperating
entities. For more information about the memorandum of understanding, see
part 606. Responsibilities and
intentions towards digitizing and map finishing are part of a soil survey area MOU or an amendment to an MOU.
- To acquire imagery for an initial soil survey:
- The MLRA Region-wide memorandum of understanding, approved by the Director, Soil Survey Division,
must be on file at the National Soil Survey Center and the National Cartography and Geospatial Center.
Optional memoranda of understanding for intial soil surveys and for update soil surveys that require
extensive revision may also be on file. Refer to
part 606.01.
- Use the on-line NCGC Ordering System at http://www.ftw.nrcs.usda.gov/ncgcos
to acquire imagery from the National Cartography and Geospatial Center. The ordering systen was
developed to streamline the process of ordering products and services from NCGC. The NCGC Ordering
System replaces the Carto-19. Items such as imagery and orthophotography, map compilation materials,
publication of soil survey products, SSURGO and digital map finishing standards, and status graphics
are available throughthe on-line ordering system
- To acquire imagery for a soil survey update:
- Send a written request to the National Soil Survey Center from the MLRA regional office and
the state conservationist for approval to update a published soil survey. The Soil Survey Division
responds by letter to requests to update National Cooperative Soil Survey projects.
- Obtain Division approval before making any agreements that bind the Natural Resources Conservation
Service with State or local governments, universities, or other potential cooperators.
- Use the National Cartography and Geospatial Center on-line ordering system at
http://www.ftw.nrcs.usda.gov/ncgcos for acquisition
and preparation of the imagery after approvals and agreements are complete.
- Delivery Time Schedules of Imagery
- Aerial Photography – Order aerial photography for field mapping from
the National Cartography and Geospatial Center. Allow 4 to 6 months for delivery to the field office.
- Digital Orthophotography – Order digital orthophotography
from the National Cartography and Geospatial Center. Allow a minimum 13 months for delivery of a soft copy of
the digital orthophotography and 16 months for a hard copy reproduction.
- Imagery Acquisition Assistance
- The National Cartography and Geospatial Center (NCGC) assists states to acquire aerial
photography and orthophotography. This assistance is available whether funding is from the states or by
the Soil Survey Division. The NCGC will:
- Provide information on imagery availability
- Order imagery
- Inspect imagery to ensure quality and coverage
- Provide digital orthophoto quadrangles on hardcopy
- Duplicate digital orthophoto quarter-quadrangles on CD-ROM media.
- Archiving
- Aerial Photography – The National Cartography and Geospatial Center does not archive
aerial photography. The Federal Records Center, Fort Worth, Texas archives the designated official field
sheets after the survey is published.
- Digital Orthophotography – The National Cartography and Geospatial Center retains
copies of all orthophotography acquired for use in the National Cooperative Soil Survey program. Reproductions
of archived digital orthophotography are available upon request the National Cartography and Geospatial Center
on-line ordering system at http://www.ftw.nrcs.usda.gov/ncgcos.
- Preparation of Maps and Mapping Material
- Index to Field Map Sheets – The National Cartography and Geospatial Center prepares an index to map
sheets for ordered photography. The format of this index to map sheets corresponds with indexes prepared
for publication of the soil survey.
The National Cartography and Geospatial Center includes a title block and special notes to aid the
user in interpreting the information on the index to map sheets.
- Field Mapping Material – Field mapping material can include aerial photography on paper or film positives.
Aerial photography is available at publication scale.
- Publication Index to Detailed Map Sheets – The National Cartography and Geospatial Center prepares an
index to map sheets for orthophotography ordered for publication of soil surveys. Copies of the index accompany
the compilation material sent to the state office.
The Center stores the original index to map sheets with the halftone negatives and use them to prepare the
index to map sheets for the publication of the soil survey. The Center prepares a press ready index when they
receive the request for index maps via the National Cartography and Geospatial Center on-line ordering system
at http://www.ftw.nrcs.usda.gov/ncgcos This occurs before
completion of the final publication negatives.
- Publication Compilation Material – The National Cartography and Geospatial Center prepares compilation
material for publication of the soil survey. Compilation material may include:
- Photobase positive – a halftone film reproduction made from the halftone negative. The
NCGC punch registers the photobase positive with the halftone negative, using a Hulen punch
registration system. When the soil survey boundary coincides with state, county, or national boundaries,
the Center draws these boundaries using information from topographic quadrangles. If the limit of the
soil survey does not coincide with boundaries on the topographic quadrangles, the ordering office must
draft the boundaries on the topographic quadrangles and supply them to the National Cartography and
Geospatial Center along with the request for ordering mapping and publication material. The proper
location of the soil survey area boundary ensures adequate coverage of the publication material and
proper placement of the boundary on the photobase positives. Add join notes and grid coordinate values
to the photobase positives as needed.
- Mylar
- Envelopes
- Index to map sheets
- Acetate
The National Cartography and Geospatial Center
considers the positive, index to map sheets, and
envelopes as a complete set of publication compilation
materials.
Compilation (647.03)
- Memorandum of Understanding
The memorandum of understanding describes who will perform the map compilation,
digitizing, and map finishing of the soil survey. This document also identifies the map scale, publication
format, the minimum size delineation to be mapped, and the publication due date. If a significant change is
made to the work or work area, the originator of the memorandum of understanding prepares an amendment to the
memorandum of understanding. See part 606 for more information.
- Classification and Correlation Document
The classification and correlation document identifies all approved map information
that will appear in the publication. It provides a conversion legend of field map unit symbols to publication
symbols; specific instructions for compiling, digitizing, and map finishing; and the Feature and Symbol Legend
for Soil Survey (NRCS-SOI-37A, Exhibit 627-5). See
part 609 for more information.
- Identification Legend
The identification legend consists of map unit symbols and map unit names. Map unit
symbols combine alpha, alphanumeric, or numeric characters. Map unit symbols uniquely identify delineations on
the map to descriptive and tabular information in the soil survey publication or database.
Part 627.04(e)(1)
provides development guidelines for the map unit symbols and names. In discussions concerning soil survey map
development, the terms “descriptive labels” or “labels” refer to map unit symbols of the identification legend.
The term “symbols” in the context of maps refers to specific features in the Feature and Symbol Legend for Soil
Survey.
- Feature and Symbol Legend for Soil Survey
Each soil survey requires a Feature and Symbol Legend for Soil Survey (NRCS-SOI-37A).
See Exhibit 627-5. The Feature and Symbol Legend for Soil Survey (NRCS-SOI-37A) identifies all approved map
features that may be published in soil surveys.
Exhibit 627-5 includes the description of standard landform and miscellaneous surface features.
The soil mapper describes the ad hoc features and the size of the standard features.
Part 627.04 describes the
application and development of the legend. The MLRA soil survey office indicates on the NRCS-SOI-37A the features
that are to be compiled with a red underline or other obvious indicator. The office submits this marked copy with
the final correlation. Compilers only transfer those features that are indicated.
- Specifications
Soil survey maps provide information about soils. Cultural and hydrographic information
on maps make the soil information more useful. Cultural information on soil survey maps assists the user to
establish location. Hydrographic information provides both location and information about the landscape. Although
this information combines onto a single map for the published soil survey, it consists of separate themes; culture,
hydrography, and soils.
Each map theme may have several types of map features; area, line, or point. Examples of area features include
soil areas and water. Examples of line features are streams, gullies, small linear soil delineations, political
boundaries, and escarpments. Point features include churches, schools, and most special features, such as wet spots,
pits, small point soil delineations, and ad hoc features.
Generally, the base map for field mapping is an aerial photograph or photobase, called a field sheet. The scale
within a field sheet may vary because of differences in ground elevation and tip and tilt of the aerial camera. The
compilation process, in addition to accurately converting and transferring map information, adjusts for these
distortions.
Field sheets are the source for the location and orientation of map features. These features align as shown on
form NRCS-SOI-37A in Exhibit 627-5. Most features orient north unless otherwise indicated. The U.S. Geological Survey
(USGS) topographic quadrangles serve as guides for locating and identifying some map features. When discrepancies
exist between the field sheets and the topographic quadrangles, use the field sheets as they provide the most up to
date information. However, a set of topographic quadrangles designated as the official set contains all
updated information and corrections. If an official set of topographic quadrangles exists, it will be delivered
with the compilation materials to the appropriate persons for the map finishing process. The Instructions for
Map Compilation, Map Finishing, and Digitizing section of the Classification and Correlation document refer
to the official set of USGS topographic quadrangles. All cultural and hydrographic features (schools, religious
structures, wells, and windmills) are to be drafted by freehand or indicated by codes. The size of the symbols
should approximate the size of the symbols shown in
Exhibit 627-5, Feature and Symbol Legend for Soil Survey.
Use the following specifications for compiling map information for soil surveys.
- Cultural Features. Cultural features are administrative and
political subdivisions of constructed features. They include boundaries, markers, transportation features,
utilities, and various structures. Indicate them on soil survey maps for location purposes.
- Boundaries
- National, State, or Province
- County or Parish
- Minor Civil Division (only use in Connecticut, Indiana, Maine,
Massachusetts, Michigan, New Hampshire, New Jersey, New York, Ohio, Rhode Island, and
Vermont.)
- Reservations (national or state forest or park)(if desired)
- Limit of the Soil Survey (label) and/or denied access areas
- Field sheet and neatline
- Coordinate grid ticks and values. Place coordinate grid ticks and values during compilation
if the compiled information will be used as an interim product of soil survey. Generally placement
occurs during map finishing.
- Show coordinate grid ticks and values as UTM meters on all four sides of the map. The values
are 1,000 meters for 3.5-minute quadrangle format and 5,000 meters for 7.5-minute quadrangle
format intervals. Place so as to lessen any conflict with other marginalia.
- Indicate the latitude and longitude coordinates in degrees, minutes, and seconds at each
map corner and at the 2.5-minute tic locations.
- Public land survey system section boundary and corner tics. Generally all States that have
public land show public land information. The information includes land division corners or section
lines, section numbers, and township and range numbers and division bars. The placement of this
information is usually completed during map finishing, however, if compiled information will be used
as an interim product, place the information during compilation.
- Indicate township and range identification and division bars along the map neatline.
- Place the section numbers in open spaces as close to the center of the section as possible.
Obtain all public land information from the USGS topographic quadrangles or a more current and
precise source.
- Transportation features. Compiling roads, trails, and railroads is normally not done because
these features show on the published imagery. Use of the appropriate emblems or names for interstate,
Federal, state, and county roads is recommended. Place the emblems directly on the feature they
represent.
- Located Objects. Located objects are optional locational aids.
- Airport and landing field. Label with the proper name, use the term Airport, or place the
symbol for the feature.
- Cemetery. Label with the proper name, use Cemetery or Cem, or place the symbol for the
feature.
- Church. Only show where it is significant as a locational aid.
- Farmstead. Only show where it is significant as a locational aid.
- Lighthouse. These features are towers or other structures displaying a light for the guidance
of mariners
- Located object. Only show this feature in remote areas that have few or no other locational
features. Label with a descriptive label.
- Lookout tower. Only show a lookout tower in remote areas that have few or no other locational
features.
- Oil or gas well. Oil or gas wells are pits or holes dug or bored into the earth for the
extraction of oil or gases.
- Other religion. Other religion refers to sites with religious significance. Do not include
the religious denomination in the descriptive label.
- School. Only show where it is significant as a locational aid.
- Sample sites. These may be compiled but not published.
- Tank. Tanks are storage units for water or petroleum. Label as to type.
- Windmill. Show a windmill associated with a well as a windmill, and omit the well symbol. If
it is geothermal, do not show it.
- Hydrographic Features. Hydrography is information about flowing and standing water.
Compile hydrography to conform to the photobase imagery.
Where a hydrographic feature is wide enough that the actual width can be shown, compile the shoreline
or each bank as a soil delineation boundary and label with the appropriate map unit label. The shoreline
corresponds to the normal stage of water, which is usually marked by a line of permanent land vegetation.
The determination of this map unit boundary is a responsibility of the project leader. Areas covered by
shallow water may be map unit components that are not water.
Do not label large water areas as Water. Place the proper name inside the feature, if possible; otherwise
place it outside. Always use the appropriate map unit label.
The compiler is responsible for drafting any additional bodies of water visible on the photobase map
that are not delineated on the field sheets. These delineations are map units and therefore must coincide
with the legend, minimum size, requirements, and meet approval of the project leader.
Show a sewage lagoon, industrial waste pond, fish hatchery, or other miscellaneous water area, as a map
unit with a map unit label that identifies the area from other water. In addition, use the labels Sewage
Disposal Pond, Industrial Waste Pond, or Fish Hatchery.
- Drainage end. Drainage ends indicate the direction of flow. Compile the feature where streams
end abruptly and disappear into caverns, depressions, marshes, or other areas where the stream is no
longer clearly evident.
- Perennial stream. This is a stream that flows throughout most normal years. Compile this
solid line feature for a stream that is greater that 0.5 inch in length. Either indicate PSDR or note
on the margin that all streams are perennial where not indicated (and then label those that are
intermittent as INDR).
- Intermittent stream. This is a stream that is dry for a large part (more than 3 months) of
each year. Compile this solid line feature for a stream that is greater than 0.5 inch in length. Indicate
INDR or note in the margin that all streams are intermittent (and then label those that are perennial as
PSDR).
- Unclassified stream. This is a stream that is not distinguished as either perennial or
intermittent. Compile this solid line feature for a stream that is greater than 0.5 inch in length.
Label as UCDR.
- Perennial drainage or irrigation ditch. This is a perennial drainage or irrigation feature.
Compile the solid line with an arrow feature to indicate a feature that is greater than 0.5 inch in
length. Label DDIT or note use in the margin.
- Intermittent drainage or irrigation ditch. This is an intermittent drainage or irrigation
feature. Compile the solid line with an arrow feature to indicate a feature that is greater than 0.5
inch in length. Label IDIT or note use in the margin.
- Unclassified drainage or irrigation ditch. This is an unclassified drainage or irrigation
feature. Compile the solid line with an arrow feature to indicate a feature that is greater than 0.5
inch in length. Label UCDIT or note use in the margin.
- Flood pool line. Some reservoirs require a maximum flood pool boundary. For these reservoirs,
compile the soil boundaries and drainage lines to the normal reservoir shoreline. Obtain the location of
the flood pool line boundary from the topographic quadrangles, the field sheets, or both.
- Spring. Water seeps or flows from the ground naturally in these places. Only show large and
important springs on the soil map in well-watered areas. Because of their vital importance to land use
management in arid and semiarid regions, locate and compile springs with great care. These springs
usually have names that should appear on the soil map.
- Wells. These features are pits or holes dug or bored into the earth for the extraction of
water. Artesian wells are deep-bored wells in which water rises under pressure from a permeable stratum
overlaid by impermeable rock. Most irrigation wells use pumps rather than gravity flow to extract water.
The importance of wells and water tanks depends upon the soil use in the area. Show wells in arid and
semiarid regions. They may or may not exhibit surface flow.
- Soil survey features. Soil survey features include the delineations of soils or
miscellaneous areas, the soil labels, ad hoc features, and standard landform and miscellaneous surface
features. Ideally, while mapping, the soil scientist indicates only the features that appear on the legend and
will appear in the publication.
Some soil surveys require consolidating map units for correlation reasons, but extent of the map unit
should not be one of the reasons. Use standard or ad hoc features for surface located contrasting conditions
that affect use and management and that are important for locational purposes. Standard and ad hoc features are
not substitutes for describing components of map units.
The soil scientist indicates on the field sheets only the appropriate amount of detail and the features that
are necessary for publication. Any detail beyond this clutters the field sheet, may result in incorrect soil
information because of compilation decisions, and increases the cost of map preparation and publication.
Compilers maintain registration of field sheet information and the compilation base throughout the soil line
transfer process. They adjust the compilation base as the transfer progresses to ensure accurate location of
soil area boundaries. Depending on the amount of displacement present in the field sheets, the adjustment may
be minor or quite significant. Generally, nominal scale field sheets require much more adjustment during the
compilation process than orthophotography used as field sheets.
- Soil delineations and soil symbols
- Area soil map unit delineations.
Soil area boundary lines encircle all soil and miscellaneous areas (including water) that are
identified as polygons. Compilers accurately transfer soil area boundary lines from field sheets to
stable base media compilation base. They match and extend all feature edges across the neatline of
all adjoining sheets to ensure accuracy in the joining.
After compiling all hydrographic and cultural features onto separate overlays, compilers transfer
soil area boundaries onto a third overlay and letter the soil map unit labels that have been approved
for publication. They draft all compiled items with sufficient clarity to permit easy and accurate
legibility for later interpretation.
All soil area boundary lines will be smooth, solid lines with consistent line width without skips
or overlaps. Generally adjust soil area boundary lines to avoid coinciding with other compiled
features. Line features that are used to identify soil area boundaries may coincide with hydrography
features.
Do not terminate soil area boundary lines on other compiled features, except on neatlines in
cases where the neatline is the limit of the soil survey.
In some cases, one publication or approved soil label represents several different soil labels
shown on the field sheets. Where this occurs, consolidate adjoining areas of the same label into one
soil area. Delete the common soil area boundary line between soil areas combined in this manner.
Smooth or round any sharp or irregular delineation resulting from this combining.
- Point or line segment soil map unit delineations.
Use point or line segment soil map unit delineation features to indicate very significant soil
areas that are too small to be shown as soil area features (polygons) at the scale of mapping. Be
sure to accurately match the line segment feature to the adjoining map sheet to ensure accuracy in
joining.
The line segment soil map unit delineation feature has precedence over the hydrography feature.
- Other soil survey features.
Some soil map features are too small to be delineated as areas at a given scale and are
represented as either standard landform or miscellaneous surface features or as ad hoc features.
These areas are not significant enough to warrant the assignment of a map unit symbol, nor described
or interpreted. They generally are observable from the surface. They are locational aids and highlight
uncommon occurrences of soil survey features.
Each standard landform or miscellaneous surface feature has a standard description and symbol.
Their size is set in terms of acres by the mapper. Refer to the Descriptions of Standard Landform and
Miscellaneous Surface Features and Descriptions for Ad hoc Features on the back of NRCS-SOI-37A
Exhibit 627-5.
In addition, approved marker symbols may be used for special purposes, but their use is not
standardized. They have unique definitions and sizes for each soil survey area. These special purpose
symbols represent ad hoc features.
When indicating ad hoc features, use only approved symbols. Use symbols that do not look similar
to other symbols used in the legend. The approved symbols for ad hoc features are shown on
NRCS-SOI-37A in Exhibit 627-5.
Compile all symbols for soil survey features to the compilation base in the exact location
portrayed on the field sheets. Orient symbols for soil survey features to north.
- Soil labels. Include at least one soil label in each soil area, or attached to each point or line
segment soil map unit delineation feature. Use the conversion legend (included in the classification and
correlation document) to select the correct soil label when converting field to publication labels. If,
during the compilation process, there are labels on the field sheets that are not found on the conversion
legend, the project leader will determine the disposition of the symbols. They may need to be added to the
legend and final correlation document. Account for every soil label during the correlation process. When
making the soil maps in the field, use the correlation process for documenting the disposition of all soil
labels. Do not change the soil labels for map units that are combined into other units while the mapping is
progressing. Attempting to change the labels rather than correlate them usually results in some labels not
being changed. This provides an untimely discovery at compilation of labels that do not appear on the
conversion legend.
The MLRA regional office is responsible for the conversion of all labels to either the publication labels
or to the legend in the signed classification and correlation document and amendments.
Position soil labels horizontally, space permitting, as near to the center of the delineated area as
possible. Where soil areas are large and irregular, place more than one soil label to permit easy
identification of the area. Avoid placing soil labels where the publication image is dark, e.g. wooded areas.
When an area is too narrow to accommodate a label placed horizontally, place it at an angle or vertically.
Do not allow soil labels to touch or be placed too close to the soil boundary or any other labels. A good
rule to follow is to leave a space the width of a soil area boundary line between labels or lines. Place
soil labels over streams only if the soil area is long and narrow and space does not permit locating the
label horizontally.
Other soil survey features are not labeled, but are accurately located on the map with the appropriate
marker symbol.
- Leaders. Only use leaders to connect soil area boundaries to their label when absolutely necessary. If
you must use them, do not allow them to cross more than one soil boundary or interfere with any other
labels or features. Extend the leader into the soil area so it does not touch the opposite side of the soil
area. All point and line segment soil map unit delineation features require a leader to the label.
- Coinciding Map Features
The USGS topographic quadrangles are the source for locating boundaries. However, if
any of the boundaries on the topographic quadrangles are out of date or incorrect, indicate the correct location
on the field sheets. Also make a notation of the discrepancy in Instructions for Map Compilation, Map Finishing,
and Digitizing in the classification and correlation document and on the official set of USGS
topographic quadrangles. Maintain uniformity in line spacing, widths, lengths, and symbolization throughout the map
compilation assignment.
- When two or more map features fall in the same location on a map sheet, the priority for showing these
features are shown in Table 1.
Table 1 Priority for showing coinciding map features
| Priority |
Feature |
| 1 |
Road |
| 2 |
National boundary |
| 3 |
State boundary |
| 4 |
County or parish boundary |
| 5 |
Reservation (national or state forest or park) |
| 6 |
Limit of soil survey boundary |
| 7 |
Minor civil division boundary |
| 8 |
Public Land Survey System Section Boundary |
| 9 |
Neatline |
- Features prioritized as 1 through 8 always precede the map neatline. If such situations exist, do not
remove the neatline from the compilation base; instead, indicate these features on top of the neatline.
- Compile all hydrographic features even if they coincide with prioritized features, removal should only
be done during map finishing.
- Point or line segment soil map unit delineation features precede hydrographic and other prioritized
features. Move soil area boundary lines so that they do not coincide with compiled features.
- Lettering
Legibility and consistency of lettering are the most important criteria for making a
legible map. Specifying size of lettering is difficult because there are a number of circumstances that make this
impractical. The density of soil area boundary lines and the presence of hydrographic and cultural features are
some of the items that determine the letter size limitations. Generally, lettering height of soil labels is no
less than 0.05 inch nor more than 0.15 inch. The lettering style is simple and legible. Avoid fancy or artistic
styles. Use the single stroke, either slant or vertical. It most nearly approaches the strokes ordinarily used in
writing, adapts itself to small space, can be photocopied, condensed or expanded without affecting the legibility,
and is easy to use.
Freehand letter all names in upper and lowercase. Specific type styles and sizes for hydrographic, hypsographic,
and place names are not required on the compilation documents. Use freehand vertical lettering for all features
other than transportation and hydrographic features, which are freehand slant lettered. The main requirements are
that all lettering be neat, legible, accurate, complete, and consistent.
Unless otherwise specified in the Instructions for Map Compilation, Map Finishing, and Digitizing in
the classification and correlation document, compile names shown on the field sheets and USGS topographic quadrangles
onto the compilation bases. Where discrepancies between the field sheets and topographic quadrangles exist, use the
name on the topographic quadrangle. An exception is when, during the mapping process, names or features that are
obsolete or incorrect have been crossed out and the corrections indicated in red ink on a set of topographic
quadrangles for compilation use. Send this set of corrected topographic quadrangles with the compilation materials
for use in the map finishing process.
Position all lettering to read from left to right or from bottom to top of the compilation base. Use the USGS
topographic quadrangles for locating features being named. Place all cultural names, road numbers, and soil labels
horizontal to the north and south neatlines. Position hydrographic, hypsographic, road, and railroad names in
alignment with the features they identify.
- Quality Control and Assurance
- The MLRA regional office is responsible for compilation and its quality assurance. The MLRA soil survey
office, or other office doing compilation, is responsible for a 100 percent edit of the compilation and the
MLRA regional office assures the edit with a 10 percent check before its release for digitizing or finishing.
- The MLRA soil survey office or compiling office carefully reviews, edits, and properly matches all data
(100 percent) from one compilation sheet to another.
Exhibit 647-1 provides a compilation edit checklist.
- The edit checklist and editorial symbols when used with the overlay provide a useful tool in identifying
the most common errors that occur in a given soil survey area. This information can be helpful, to both the
soil scientists that performed the mapping or the individual responsible for the compilation, in providing
feedback as to where improvements are needed to make a high quality soil map. If the compiler is not a soil
scientist, a soil scientist should resolve all soil related errors that are identified during the edit process.
- Refer to Exhibit 647-2 for a list identifying common kinds of errors and the recommended editorial symbols
indicating the actions needed to correct the errors.
- After correcting all edit errors, the MLRA regional office completes the Map Compilation Certification
shown in Exhibit 647-3.
Compilation Techniques (647.04)
Request the latest compilation techniques from the National
Cartography and Geospatial Center.
Recompilation for Digitizing (647.05)
- Planimetric Correct Base
Digitizing standards require a planimetric correct base. Recompile published soil surveys
to a planimetric correct base, typically orthophoto quadrangles, on stable mylar before or during digitizing.
- Line Adjustment
Use remote sensing techniques that capitalize on the improved base photography,
topographic contour features, and stereographic photographs to improve line placement, and thus create a more
accurate soil map. Improved placement of a soil delineation results in a slight to significant adjustment from the
original soil map in the published report. Reasons for line adjustment are the improved quality of the orthophoto
tones, correction of obvious discrepancies between soil delineations and topographic contours, and edge matching.
- Documenting Changes in Line Placement
Document changes in line placement and, if needed, provide a supplement of differences
from the published soil survey maps to the digitized soil maps. These guidelines also apply to the digitization of
parts of soil surveys, such as a local watershed or river basin project.
- Minimal Requirements
- Memorandum of Understanding. Reference to
part 606.01(a)(6) of the National Soil Survey
Handbook. Append the existing soil survey memorandum of understanding with amendments concerning the digital
product. Those cooperators that signed the original memorandum of understanding are to review and sign the
amendment. Address the following items in the amendment.
- Purpose - Specify the reason(s) for recompilation before digitizing, such as enacting an
exact join, improved photographic tones, more recent photographic image, corrected base, or more suitable
scale.
- Cooperating agencies and their responsibilities - Identify the cooperators and define their
roles in recompilation and digitizing.
- Specifications and procedures - Explain the procedures to compile and digitize the soil
survey or parts thereof. Identify the materials used in the procedures and discuss the general kinds of
adjustments that are anticipated in the placement of soil boundary lines. To easily differentiate from
the original delineations, specify that line edits will be made to contrast (red ink) with line work of
the published soil survey.
- Include the statement - “Maps produced from the new digitized map will be designated the
official copy of the soil survey for the NRCS field office technical guide. A record of line edits will
be on file for review upon request.”
- Include the statement - “The soil survey will be digitized according to SSURGO standards and
archived at the NRCS National Cartography and Geospatial Center. The digitized soil survey will not be
copyrighted and NRCS reserves the right to archive and distribute data generated under the terms of this
amendment for their use.”
- Identify plans - Identify plans to supplement the published soil survey, or state that no
supplement will be issued.
- Supplement to a published soil survey map. All supplements will
be available to users of soil survey information. The supplement may include the following.
- Narrative explanation - Provide a narrative that explains deviations from the published
report from digitizing. State in the narrative that “photocopies of edited portions of map sheets are
available for review.” Statements included in the supplement would be different if soil lines were
recompiled to stable base USGS topographic quadrangles rather than orthophotos or orthophoto
quarter-quadrangles. See Exhibit 647-4 for a sample narrative explanation.
- Errata sheet - The errata sheet can either be a list of legal descriptions (e.g., Sheet 13,
N.W. ¼, Sec. 32) or a thematic map showing the geographic location, to the quarter section or an
equivalent, of each edit. An index to map sheets, shaded to depict the areas where changes occur, may
be used.
- Edited map sheets for distribution - Edited map sheets that are developed for distribution
must be of professional quality. States preference will dictate the kind of map product developed. The
National Cartography and Geospatial Center can provide copies of digitized full map sheets with an
orthophoto background. Reproductions by the National Cartography and Geospatial Center are on a
reimbursable basis. Another option is to provide photocopies of portions of published soil maps showing
only where significant changes to line placements have been made.
- Classification and correlation document. An amendment to the soil survey classification and
correlation document is required if map unit names or symbols, including symbols for ad hoc features, have been
converted, added, deleted, or revised. If map units are recorrelated or added, they must be accordance with
General Manual, Part 402.5.
- Source Materials Required For Digitizing
The following materials and documents should be available at the time of digitizing:
- Soil legend - An itemized listing of all soil map symbols and names to be digitized.
- Soil map - Soil maps showing cultural features, hydrographic features, soil area boundaries, point and line
segment soil map unit delineations, soil map unit labels, standard features, and ad hoc features.
- Map indexes - An index to soil maps and USGS topographic quadrangles or orthophoto quadrangles.
- Published soil survey maps - Copies of the original published soil survey maps.
- Soil classification and correlation document and amendments - An approved document is required before a
soil survey is contracted for digitizing.
SSURGO Characteristics (647.06)
The SSURGO database is:
- Defined in a memorandum of understanding.
- Mapping on hard copy aerial photography, subsequently compiling to orthophotography, and hand- or scan- digitizing
are avoided if at all possible. Field mapping is done using electronic media and on-screen digitizing as much as
possible to avoid these extra steps.
- If (b) above is not possible, map on orthophoto 7.5 minute quadrangles or orthophoto 3.5 minute quadrangles or
compile onto one of these bases before or during digitizing. USGS 7.5-minute topographic quadrangles or SPOT quadrangles
may also be used if orthophoto quadrangles are not available.
- Mapped at scales ranging from 1:12,000 to 1:63,360.
- Supported by an approved and signed classification and correlation document and amendments.
- Digitized by raster scanning and vector conversion or line-segment (vector) methods.
- Captured or converted to a Geographiccoordinate reference system, decimal degrees map units, and a North American
Datum of 1983 with a Geodetic Reference System of 1980 spheroid or a North American Datum of 1927 with a Clarke 1866
spheroid.
- Geo-referenced digital spatial data, tabular data, and metadata.
- Spatial data stored in a vector data structure.
- Archived in a seamless survey area.
- Within digitizing standards and specifications of NRCS.
Digitizing Specifications (647.07)
- Base Map Characteristics
The soil survey base map must meet the following characteristics.
- Maps to be used. Base maps used for digitizing soil surveys must meet National Map
Accuracy Standards. 7.5-minute orthophoto quadrangles, 3.75-minute orthophoto quadrangles, USGS 7.5-minute
topographic quadrangles or SPOT quadrangles meet these standards. Base maps produced from digital
orthophotography to the National Standard for Spatial Data Accuracy are also acceptable. Base maps are to be
on stable material to minimize distortion caused by contracting and expanding from changes in temperature and
humidity. Mylar material that is 0.004-inch (4 mil) thick is suitable under normal stable environmental
conditions. Generally humidity fluctuations affect mylar stability more than temperature fluctuations.
Soil surveys not mapped on a base that meets map accuracy standards are recompiled onto an accurate base
map before or during digitizing. If the soil survey is mapped on an accurate mylar base map, only the accurate
conversion of soil map unit symbols and standard and ad hoc features to those on the publication legend is
necessary. If the soil survey is mapped on rectified aerial photography, the accurate transfer of boundaries
onto one of these base maps is necessary to correct for ground relief distortion before or during digitizing.
The use of 1:12,000 or 1:24,000 digital orthophotography is strongly encouraged.
- National Standard for Spatial Data Accuracy. These standards define spatial accuracy as it
pertains to map products at scales of 1:250,000 and larger produced by Federal agencies. They supersede the
National Map Accuracy Standards issued June 10, 1941, and most recently revised on June 17, 1947, by the former
U.S. Bureau of the Budget.
These standards are the measure of positional accuracy of map features (the difference between their map
position and where they actually occur on the ground). Soil surveys will be digitized only from base maps that
meet these standards.
- Horizontal Accuracy - The standard error, or root-mean-square error, is measured separately in
both the x and y coordinates at the publication scale (Table 2).
- For Class 1 maps, the standard error shall not exceed ± 0.25 mm.
- For Class 2 maps, the standard error shall not exceed ± 0.50 mm.
- Maps that exceed ± 0.50 mm do not meet National Standard for Spatial Data Accuracy.
Table 2. Horizontal accuracy limits at ground-scale.
| Scale |
Limits for x or y meters (ft) |
| Class 1 |
Class 2 |
| 1:12,000 |
±3.0m (10) |
±6.0m (20) |
| 1:24,000 |
±6.0m (20) |
±12.0m (39) |
| 1:63,600 |
±15.8m (52) |
±31.6m (104) |
- Vertical accuracy - The following limits of accuracy apply to contour maps and to maps showing
spot elevations.
- For Class 1 maps, the standard error of elevations determined from the contours shall not exceed
one-third of the contour interval.
- For Class 2 maps, the standard error shall not exceed two-thirds of the contour interval.
- Maps with elevations that exceed the Class 2 criterion do not meet National Standard for Spatial
Data Accuracy.
- The standard error for spot elevations (heights) shall not exceed one-sixth of the published or
planned contour interval.
- Accuracy Test - The allowable limits are expressed in millimeters at the product scale, rather
than ground scale.
- Certification of products shall be based on both horizontal and vertical tests, unless contours or
spot elevations are not shown, in which case certification shall be based only on horizontal tests.
- All map measurements will be made on stable base materials.
- The horizontal and vertical accuracy tests shall each have a minimum of 20 and not more than 50
well-defined test points, well spaced and spread over the project as evenly as is economically
possible.
- Maps in which the vertical or horizontal standards are impractical to meet are considered to fail
standards for that dimension of the standards not tested.
- When testing a sufficient number of maps (3%) in a series is impractical to determine whether the
series as a whole passes or fails, then all maps in the series shall be labeled as not tested.
- Compute standard errors by comparing the positions or elevations of points with corresponding
positions or elevations as determined by surveys of a higher accuracy.
- Calculate the standard error separately for the x and y coordinates and for vertical test points
using all the test points.
- Determination may be made without a formal test when the product is derived using larger scale
products or products known to meet these standards, or by error propagation analysis that clearly proves
conformance.
- The limits of accuracy apply in all cases to positions of well-defined points. Well-defined points
are features, such as road intersections or road and railway intersections that can be accurately
identified and located at discrete positions.
- Product Identification - Label products with a two-part label; if elevation information is not
shown, label products for horizontal accuracy only.
- If both horizontal and vertical pass, label:
- “Complies with National Standard for Spatial Data Accuracy (Horizontal), Class __”
- “Complies with National Standard for Spatial Data Accuracy (Vertical), Class __”
- If either or both are tested, but fail, replace appropriate line or lines as shown below. Insert
Horizontal, Vertical, or Horizontal and Vertical as appropriate.
- “Does not meet National Standard for Spatial Data Accuracy (______)”
- If either or both are not tested, replace appropriate line or lines as shown below. Insert
Horizontal, Vertical, or Horizontal and Vertical as appropriate.
- “Not tested for Compliance with National Standard for Spatial Data Accuracy (______)”
- Series Maps - At least 100 maps are made using similar source material, instruments, and
procedures.
- The class of a series of maps may be determined by testing a limited number of individual maps from
the series.
- At least 3 percent (but not less than 10) individual maps must be tested.
- The class into which 90 percent of the standard errors of the individually tested maps fall will
apply to the entire series.
- Reference System. The horizontal control for the SSURGO database is the North American
Datum of 1983 or the North American Datum of 1927 and is determined by the compilation base.
- Map Sheet Formats. Soil surveys mapped on the ½ or 1/3 orthophoto quadrangle formats can
be digitized in these formats; however, soil digital data sets provided to the NRCS must be merged and formatted
in a 7.5-minute quadrangle format. Soil surveys mapped on 3.75-minute orthophoto quadrangles do not need to be
merged into a 7.5-minute quadrangle format. The map base for the final product of all soil surveys will be on
orthophoto quadrangles at a standard map scale of either 1:12,000 or 1:24,000.
- Features To Be Digitized
Area soil survey features and linear and point soil survey features are digitized as
three separate layers.
- Layer 1
- Examples of area features are soil and water areas. These features are composed of soil boundary
lines or other boundary lines such as a double line stream or limit of soil survey that form polygons
and occupy area.
- Layer 2
- Examples of soil line segments are narrow elongated riparian areas.
- Examples of soil point features are small circular riparian areas.
- Layer 3
- Examples of special linear features are escarpments and gullies.
- Examples of special point features are landform features, miscellaneous surface features, and ad hoc
features sometimes known as spot symbols. Wet spots, pits, and sinkholes are specific examples of these
features.
Both linear and point special features represent areas that are too small to be digitized as
polygons (area features smaller than 0.5 cm in diameter).
- Data Capture
The following standards and specifications apply to digitizing soil surveys at scales
from 1:12,000 to 1:63,360.
- Soil and Water Boundaries.
- Digitize each soil or water boundary within a 0.01-inch (0.254 mm) line width of the source
document. Follow the centerline of the boundary. Represent each boundary with no greater number of
coordinate pair vertices, than is necessary to record the boundaries within the 0.01-inch (0.254 mm)
accuracy limit.
Digitize “islands” as a continuous line segment with only a beginning and ending node.
Connect beginning and ending points of each digitized line at a common intersecting point with another
soil boundary, water boundary, or limit of soil survey boundary.
- Limit of Soil Survey. Digitize each soil survey area boundary within a 0.01-inch (0.254 mm)
line width of the source document. Follow the centerline of the boundary. Represent each boundary with no greater
number of coordinate pairs, vertices, than is necessary to record the boundary within the 0.01-inch (0.254 mm)
accuracy limit.
- Geographic Control. Establish geographic control using the four corner coordinate values of
the 7.5-minute topographic quadrangle, 7.5-minute orthophoto quadrangle, or 3.75-minute orthophoto quadrangle.
- Nodes. Digitize nodes at the intersection of soil lines and at the endpoint of lines where
they join.
- Linear Features. Digitize linear features as a single line within a 0.01-inch (0.254 mm)
line width of the source document.
- Point Features. Digitize point features as a single coordinate pair within a 0.01-inch
(0.254 mm) distance of its location on the source document.
- Legends
- Area Features
- The soil map symbols in the legend in the classification and correlation document and amendments.
- Permanent water and miscellaneous water will
conform to soil map unit labels (i.e. alpha,
numeric, or alphanumeric)
Table 3 shows an example of an approved correlation legend.
Table 3. An approved correlation legend
| ApB |
Alpha silt loam, 1 to 3 percent slopes |
| Ba |
Barney loam, very stony |
| Be |
Beta silt loam |
| Go |
Gomer clay, frequently flooded |
| Md |
Madras loamy fine sand |
| W |
Water |
| We |
Wehadkee fine sandy loam |
- Point and Line Segment Soil Map Unit Features
The soil map symbols in the legend in the classification and correlation
documents and amendments.
- Linear and Point Special Features. Digitize the soil survey standard and ad hoc features
identified in Exhibit 627-5, NRCS-SOI-37A Feature and Symbol Legend for Soil Survey if they are identified in
the classification and correlation document and amendments. Table 4 shows an approved feature and symbol Legend.
Ad hoc features follow standard landform and miscellaneous surface features on the legend.
Part 647.08 describes
how to assign labels to the ad hoc feature.
Attribute the features with the descriptive labels during data capture.
Table 4. An approved soil survey features correlation legend
| CLA |
Clay spot |
| GPI |
Gravel pit |
| ROC |
Rock outcrop |
| SLP |
Short, steep slope |
| STV |
Very stony spot |
| WET |
Wet spot |
| BOG |
Area of acid organics |
- Labeling
- Descriptive Labels. Label each polygon with a descriptive label. The descriptive labels
are identical to the map unit symbols in the approved soil classification and correlation document and amendments.
This includes symbols for map unit delineations, standard features, and ad hoc features.
- Label Position. Position the coordinate point for the map unit label at or near the
centroid of the polygon. Move the coordinate point into the area if the centroid falls outside of the polygon.
Centrally locate the coordinate point for linear and point features on the feature.
- Special Labels. Special labels are assigned during digitizing to areas that were not
compiled with map unit labels. If they are assigned, they should be added to the classification and correlation
document. Special labels are listed in the mapunit table in NASIS so that a mukey can be generated for them. As
such, they will be included in the map unit legend legend.
- Label areas not yet mapped or digitized as part of a progressive survey NOTCOM
for not completed.
- Label area outside the limit of the soil survey area boundary, but within the neatline BLANK
- Label large concrete or riprap covered dams DAM and large levees LEVEE when unassigned.
- Label water areas (ponds, lakes) with the symbol that has been assigned. If the areas are not
assigned, label the water area as W or M-W if a miscellaneous water area.
- Label map features crossing into adjacent map sheets with the same descriptive labels.
- Label areas DA that are unmapped because of denied access.
- If the map unit symbols are numeric, then the symbols are assigned numeric values except BLANK and NOTCOM.
- Spatial Data Format
- Spatial Format. Digital soil data sets are in a seamless survey area format.
- Internal Spatial Reference. Coordinate values can be collected in any internal coordinate
system during the digitizing process.
- External Spatial Reference. The following coordinate reference system is required for all
coordinate data:
- Ground based system and projection are Geographic.
- Map units are in decimal degrees.
- An ArcInfo coverage is the format imported into the Soil Data Warehouse. Horizontal datum is the
North American Datum of 1983 that is based upon the Geodetic Reference System of 1980 spheroid or the
North American Datum of 1927 that is based upon the Clarke 1866 spheroid. The reference system is the
same as the digitizing base.
- No x_ or y_ coordinate shifts (offsets) are permitted.
- Format of data coordinates is real.
- Data Structure. Map data are in a vector structure (i.e., location of lines, points, and
area boundaries are represented as strings of x, y coordinate pairs).
- Spatial Data Files Naming Convention
- The naming convention for SSURGO spatial files is the 2-letter state abbreviation followed by the FIPS code.
Each geospatial layer has its own designation.
- a – soil polygon coverage
- b – soil survey boundary coverage
- c – linear soil map unit coverage
- d – point soil map unit coverage
- l – linear special feature coverage
- p – point special feature coverage
- q – quadrangle coverage
- An example of the soil polygon coverage name for Henry County, Virginia is VA089_a.
- Tabular Attribute Data
The MLRA regional office certifies the tabular attribute data to be current and accurate.
Current and accurate data are current with the soil classification and correlation document and amendments, and they
are identical to the data downloaded for use in the Field Office Technical Guide. The reliability of the individual
data elements and tables are to be addressed in the metadata file if necessary.
The exportcertdate column in the distlegendmd Map Unit Record table is defined as the mm/dd/yyyy the data for
the soil survey area was certified by the MLRA regional office as edited and available for public use. This column
must be populated when submitting the tabular data. This is essential for dating the tabular data, which are
periodically updated.
- Map Unit Record Database. Each map unit symbol contained in the spatial data must have a
matching symbol in NASIS. It is acceptable for extra symbols to be in the NASIS data that are not in the spatial
data.
- Soil survey features. Prepare and archive a soil survey features file for the SSURGO
database. The name of the file will be “feature.” The format is a variable record length ASCII text file. The
first row contains the name of each column, feat_label, feat_name, and feat_desc. The second row contains at
least one dash underneath each column name. Tabs separate the column names and dashes. A return character is at
the end of each of these rows. Delimit each subsequent row by a return character and form a record in the table.
A row consists of tab delimited columns. Each row has the same number of columns as the file header (first two
rows). The file contains a descriptive label, feature name, and definition for each linear and point soil survey
feature and ad hoc feature in the legend.
- Metadata
The Soil Survey Geographic (SSURGO) product is a combination of both spatial and tabular
data. Federal Geographic Data Committee compliant metadata exists for the spatial
and tabular data. Both static and
dynamic metadata exist for the tabular component.
Metadata provide information about the content, quality, condition, and related characteristics of data. Metadata
provide information about the NRCS Soil Survey Geographic (SSURGO) database holdings to data catalogues,
clearinghouses, and brokerages. They also provide information needed to process and interpret SSURGO data received
through a transfer either by media or Internet. Metadata provide information needed to:
- Determine the sets of data that exist for a geographic location.
- Determine if a set of data meet a specific need.
- Acquire an identified set of data.
- Process and use a set of data.
- Submit metadata with the SSURGO spatial for archiving in the Soil Data Warehouse.
The template in Exhibit 647-13 is used
to create metadata. The template and
explanation of numbered blanks are available in an ASCII digital format from the National Cartography and
Geospatial Center. The name of the metadata file in the SSURGO database is the area symbol for the soil survey
area to which the dataset applies. The extension will be “.met”. For example, va001.met, is the name of the
metadata file for Accomack County, Virginia.
- SSURGO Version 2 Static Tabular Metadata. The dynamic metadata documents the contents of a particular export.
The reports and diagrams listed below document the static tabular metadata, which includes documentation of the
tables that ultimately record the dynamic tabular metadata. The following reports and diagrams are available in
Adobe Portable Document Format at
http://nasis.nrcs.usda.gov/documents/metadata/ssurgov2_0/
- Static Tabular Metadata - Domains
- Static Tabular Metadata - Tables
- Static Tabular Metadata - Table Columns
- Static Tabular Metadata - Table Column Descriptions
- Static Tabular Metadata - Indexes
- Static Tabular Metadata - Relationships
- Traditional Data Structure Diagram
- Physical Data Model
- SSURGO Version 2 Microsoft Access Template Database for Microsoft Access 97 (zipped)
- SSURGO Version 2 Microsoft Access Template Database for Microsoft Access 2000 (zipped)
- Quality Control
Quality control of soil surveys and their digitized products is the responsibility of
the office doing the work. The MLRA regional office provides quality assurance. The MLRA regional office ensures
that the digitizing source document is correct and that the digitized data match the digitizing source.
The digitizing unit performs a 100 percent edit of all materials. This includes a 100 percent hardcopy check plot
review. The digitizing unit submits materials to the MLRA regional office during the course of the work. The MLRA
regional office provides a 100 percent review of 10 percent of the digitized material. The MLRA regional office does
not provide final approval until approval by progressive correlation or by a final classification and correlation
document.
- Editing. A complete and detailed edit of the digitized data (100% edit by digitizing unit)
occurs before their release for negative preparation or for submission into the SSURGO database.
- Check Plots. Each digitized quadrangle of a soil map data set requires a computer generated
mylar check plot. The digitizing units produce the check plots. The check plots are to check line and label
accuracy with the source maps. The digitizing unit conducts this 100 percent edit. MLRA regional office
supervises or ensures this edit. Check plots require the following (the color used for the plots are optional,
they should be a different color than the compilation documents):
- Generate an ink check plot for each quadrangle with a 0.01-inch (0.254 mm) line width on stable base
mylar (minimum of 4 mil) material. Plot all data within 0.005 inch (0.127 mm) of their coordinate
locations in the database.
- Plot descriptive labels horizontally as single stroke characters with a height and width of 0.08 to
0.1 inch (2.032 mm to 2.54 mm).
- Plot the map name and scale outside of the map neatline.
- Plot area features and linear and point features either on a single plot or on separate plots.
- Plot area feature boundaries, neatlines, limit of soil survey boundaries, and descriptive labels and
other text in black.
- Plot the origin points for point features 0.03 (0.762 mm) in diameter. Plot the origin points and
their abbreviated descriptive labels in green. Offset the label from the original point such that the
label does not touch the origin point. Use the lower left corner of the first character of the
descriptive label as the point of text origin.
- Plot linear features and their abbreviated descriptive labels in green. Locate the label point at
the center of the line feature. Offset the label from the label point such that the label does not touch
the feature. Use the lower left corner of the first character of the descriptive label as the point of
text origin.
- Position the descriptive labels within the soil area so they begin within the soil area. The
descriptive labels for area features are identical to the soil map symbols shown on the
compiled/recompiled soil map. Use the lower left corner of the first character of the descriptive label
as the point of text origin.
- Plot unidentifiable feature labels as XXX in red until resolved.
- Plot the maps at the same scale and projection as the original digitized maps.
- Plot a second set of maps at the 1:24,000 (or 1:12,000) scale if the original map scale is other
than 1:24,000 (or 1:12,000). This is done after the final digitized data are accepted.
- Statistics. Generate statistics for each quadrangle in the soil survey area and for the
survey area. Generate the acreage statistics by UTM projection. In addition to quality control, acreage
statistics replace the grid dot counts or planimetered acreage normally performed. Do not submit these statistics
as a part of SSURGO. Note the discrepancies of more than 10 percent of the total between the Natural Resource
Inventory (NRI) total and spatially determined totals in the SSURGO review. The state soil scientist and MLRA
regional office leader review and decide where adjustments to individual map unit totals are needed.
Maintain and document the digitized acreage summary as “Digitized SSURGO Acreage Summary” when distributed.
Adjust the digitized acreages for the Bureau of Census water and land totals for publication. Document as “Census
Acreage Summary” when distributed. The main difference between the two acreage summaries is the water acreage.
Census water includes only water areas greater than 40 acres, and the digitized SSURGO acreage summary includes all
water. Water, a miscellaneous area, can be phased to meet the needs of the soil survey. Also broken down into
permanent water (lakes, ponds, reservoirs) and miscellaneous water (sewage lagoons, holding ponds, fish hatcheries).
- Quadrangle – As needed or requested by the State Soil Scientist or MLRA regional office,
generate acreage calculations and a total polygon (area) count for each 7.5-minute quadrangle or
3.75-minute quadrangle area feature map. Sort acreage calculations, to the nearest acre, by descriptive
labels.
- Summary - Summarize acreage data and polygon counts by descriptive labels for all 7.5-minute
quadrangles or 3.75-minute quadrangles. Use the format shown in Table 5.
Table 5. Acreage calculation and polygon count for a quadrangle
| NOTCOM |
798 |
| BLANK |
2280 |
| ApB |
1082 |
| Ba |
1920 |
| Be |
267 |
| Go |
2287 |
| Md |
115 |
| W |
101 |
| We |
198 |
| Total acres |
9048 |
| Total
polygons |
165 |
- Quality Assurance
The MLRA regional office is responsible for the overall technical accuracy of soil
surveys.
The National Cartography and Geospatial Center provides assistance to the MLRA regional office on quality
assurance review of digitized soil surveys.
Attributing Linear and Point Soil Features (647.08)
- Definition
Linear and point soil delineation features are soil
spatial areas that are too
small to delineate as polygons at the mapping scale, but are large enough and contrasting enough to significantly
influence use and management. Soil surveyors do not map linear and point soil delineations when the feature they
represent is a common component in the map unit. They name, describe, and locate features that are common components
in the map unit in the map unit description.
- Legend Development
Use a leader to attach the symbols for point and line segment map unit delineations to
the point or line segment. Correlate these symbols or labels into the soil survey area legend and handle like other
map units.
- Digitizing
For the SSURGO database, digitize all linear and point features that are mapped and
correlated.
Digital Map Finishing (647.09)
- General
The memorandum of understanding describes who will perform map finishing. The NRCS-SOI-37A
(Exhibit 627-5) in the Classification and Correlation document identifies features to appear in the soil survey
publication. Only map finish the items indicated on this approved NRCS-SOI-37A. Omission of features on the
compilation does not constitute the omission of features on the map finished maps. The MLRA regional office decides
the fate of questionable compilation map features. The MLRA
regional office has responsibility for developing, archiving,
and maintaining text layers for soil survey publication maps.
- Quality Control and Assurance
The MLRA regional office is responsible for map finishing and its quality control and
assurance. This office is responsible for ensuring a 100 percent edit of the map finishing before the final negative
preparation. The digital map finishing site is responsible for carrying out the 100 percent edit and the MLRA
normally conducts a 10 percent spot check. State offices upon agreement may share this role. A map finishing edit
checklist is provided in Exhibit 647-10. If the review is satisfactory, the MLRA Leader signs the map finishing
certification letter and ships the materials to the National Cartography and Geospatial Center. Refer to
Exhibit
647-11 Map Finishing Certification for a certification letter example. The National Cartography and Geospatial Center provides quality review assistance to the MLRA regional office.
After the MLRA regional office approves the map finished materials, they ship them to the center for final negative
preparation.
Prior to preparing the negatives, the National Cartography and Geospatial Center selects at random, a ten percent
sample of the maps. They plot the selected map files and review them for data format conformity and data accuracy.
If the review indicates that the data files are acceptable, they prepare the data as negatives.
If the review indicates that the data are not acceptable in the provided format, they return the materials to the
MLRA regional office. The MLRA regional office corrects all deficiencies before submitting the materials for an
additional sample review by the National Cartography and Geospatial Center.
Materials
- Compilation materials including the photobase maps and compilation overlays
- Index to maps
- Composite check plots for each quadrangle or quarter-quadrangle map
- Signed SSURGO certification (Exhibit 647-5) and map finishing certification (Exhibit 647-10)
documents
- Signed classification and correlation document and amendments with new NRCS-SOI-37A
- Postscript files of all publication maps on an 8 mm tape
- Specifications
Base map requirements for digital map finishing are the same as those for SSURGO
digitizing. Part 647.07(a) (1) has additional information. Generally MLRA regional offices digitize and certify as
SSURGO all surveys that are compiled to orthophotography prior to digitizing for map finishing. Soil surveys mapped
and compiled in the 1/3 quadrangle format can be digitized in this format; however, digital data sets provided to and
archived by the NRCS must be merged and formatted in a full 7.5-minute quadrangle. Soil surveys mapped on 3.75-minute
orthophoto quadrangles do not need to be merged into a 7.5-minute quadrangle format.
Develop data layers for the soil data theme and optionally for the culture and hydrography themes, as determined
by the State Soil Scientist and Memorandum of Understanding. Format these layers for archiving in modified DLG-3
optional format. Digitize data features as points, lines, or areas.
Exhibit 647-13, DLG major and minor codes for
soil survey publication features, defines the descriptive label, major and minor codes for all cultural and
hydrographic features. Derive the soil data from the certified SSURGO data. Develop text files containing additional
soil labels. Give consideration for the best placement and for the number of labels needed for each soil area.
Develop text files with proper names for cultural, hydrographic, and hypsographic features in agency supported
software.
For each published map, combine and process the data layers into two plot files in Postscript format. One plot
file contains all data to be published in blue, the other plot file contains the data to be published in black. All
work must meet the proper density, line widths, symbol, font styles, and sizes as listed in
Exhibit 647-7, Symbol and
Font Specifications. Register all work to the photobase image.
- Data Files
Develop up to four data files for each soil survey publication map. The cultural data
theme embeds the public land survey. One file of this theme contains only the public land survey section corners and
section labels and another file contains all other cultural features. The files are named with the .pf and .cf
extensions respectively. Non-public land survey areas only have one cultural data file. Develop one data file named
with the .hf extension for all hydrographic features. Two data files may exist for the soil theme. One required file
is the soil area file with the .af extension. A special feature file named with the .sf extension may exist.
- Culture. Cultural information including political and administrative boundaries,
transportation, buildings, structures, and public land survey are black on the publication maps. When two or
more boundaries fall in the same location, the Table 6 shows the priority for digitizing these features:
Table 6. Priority for showing coinciding map features
| Priority |
Feature |
| 1 |
Road |
| 2 |
National |
| 3 |
State |
| 4 |
County or parish |
| 5 |
Reservation (National or state
forest or park) |
| 6 |
Limit of soil survey |
| 7 |
Minor civil division |
| 8 |
Public Land Survey System
Section |
| 9 |
Neatline |
- Hydrography. Hydrographic information includes streams, drainage and irrigation ditches,
flood pool boundaries, springs, and wells. Streams less than 0.5 inch in length are not shown except those
connected to neatlines that extend onto the adjacent map. All hydrographic features as represented in the
“Hydrographic Features” column in the “Feature and Symbol Legend for Soil Survey” are represented in blue on
publication maps and are printed on a separate negative. Water bodies, while of hydrographic origin, are
represented on a negative containing all other soil survey information shown in black.
- Soils. Soil information includes the soil delineations, soil labels, standard landform and
miscellaneous surface features, and ad hoc features certified as SSURGO. Use a copy of the certified data to
ensure that all soil information is complete and accurate. Soil delineations include all linear and point soil
delineations as well as soil and miscellaneous areas such as gravel pit areas, water areas, miscellaneous water
areas which are further identified as sewage lagoons and filtration ponds, and double line streams and canals.
Soil area boundaries must match adjoining maps and never are broken or interrupted for any other feature.
All soil survey features are black on the publication maps.
- Text
Text includes proper names of cultural, hydrographic, and hypsographic features indicated
on published soil surveys. It also includes marginalia describing map parameters and source notes, and soil labels.
Use the USGS 7.5-minute series topographic quadrangles as guides for determining the names and locations of all text
excluding the placement of soil labels. Position all lettering so that the wording is read from left to right or from
the bottom to the top of the map. Align text with the general shape of the feature it represents, unless specified to
be placed horizontally. When letter spacing is required for effective presentation of feature names, display the text
with the letters proportionately spaced across the area to be identified. Repeat text on adjacent maps with
consistent letter spacing and size. Avoid placing text over other features whenever possible.
- Marginalia. All marginal information must be within 0.5 inch of the image area. The image
area may not exceed 25 inches (width) by 29 inches (height). Show marginal map information for each map and
include:
- agency name. Locate the agency name in the upper left corner of each map, 0.75 inch above the map
neatline and 1 inch from the map margin, in 12 point, Century condensed. Indicate as:
UNITED STATES
DEPARTMENT OF AGRICULTURE
NATURAL RESOURCES CONSERVATION SERVICE
- soil survey area title. Locate the soil survey area name in the upper right corner of each map, ¾ of
an inch above the map neatline and 1 3/8 inch below the map margin, in 12 pt, Times.
- quadrangle name. Indicate the USGS quadrangle name in the upper right corner of each map, below the
soil survey area name in 12 pt, Times.
- soil survey publication sheet number. Indicate the map sheet number on the line below the quadrangle
name in 12 pt, Times.
- USGS map series. Indicate the USGS map series below the soil survey publication sheet number in 8 pt,
Triumvirate. It is either 3.75-MINUTE SERIES or 7.5-MINUTE SERIES.
- bar scale. Indicate three separate bar in the lower center of each map. Position the first,
representing the one kilometer increment, 1 inch below the map neatline. Position a second bar scale,
representing 1000 foot increments, up to 7000, 0.5 inch below the first scale. Position a third bar
scale, representing a mile increment, 0.5 inch below the foot bar scale.
- map projection information. Indicate map projection parameters to the left of the bar scale and map
scale information in the lower center of each map. They include the UTM coordinate system and zone,
Polyconic projection, and datum. A survey area may fall within more than one UTM zone. The information
requires the appropriate zone for each quadrangle. The datum may be either 1927 or 1983 North America
Datum. The datum is the same for all maps within a survey area. Indicate all map projection information
in 8 pt, Triumvirate.
- source note. Each map requires a source note on the lower left corner of each map in 8 pt,
Triumvirate. It references contributors to the soil survey program and identifies the imagery date.
Modify it for each survey area but at a minimum include the following:
This soil survey map was compiled by the U.S. Department of Agriculture, Natural Resources
Conservation Service, and cooperating agencies. Base maps are orthophotographs prepared by the U.S. Department of Interior, Geological Survey, from _____(year)
aerial photography.
Coordinate ticks and land division corners, if shown, are approximately positioned. Digital data
are available for this quadrangle.
- Join notes. Indicate join notes identifying the adjacent sheet number and quadrangle name at the
center of each of the map neatlines, 7/8 of an inch from the map neatline, for each map in 8 pt, Univers
and in parenthesis. Orient join notes on the western and eastern sides of maps to read from bottom to
top. Use the index to map sheets to determine the adjoining sheet numbers for all maps.
- State coordinate ticks and values. State coordinate ticks and values are optional features. If shown,
the preferred system is Universal Transverse Mercator (UTM) meters. Indicate these tick values in one
thousand meter increments in 6 pt, Univers medium along the margin. Delete them if the values coincide
with other margin information. Always orient the values horizontally.
- Geographic coordinate ticks and values. Indicate the geographic coordinate values as latitude and
longitude in 8 pt, Univers medium at each map corner. The values are either the full 7.5-minute corner
values or the 3.75-minute values. In addition, for full quadrangle format maps indicate the coordinate
values representing the 2.5-minute ticks.
- North arrow. Indicate a north arrow in the lower left center of each map, positioned approximately 1
inch below the map neatline and 1 inch to the left of the neatline corner. It is 1 inch in length with
the arrow portion 0.10-inch length. Indicate the “North” in 6 pt, Truimvirate condensed.
- Land division township and range identifications and division bars. Indicate township and range
identifications on all surveys that contain these survey divisions. Indicate the values in 8 pt, Univers
medium.
- Boundary Identification
- Political Boundaries. Identify all national, state, county, or parish boundaries in 8 point
Century Schoolbook Caps placed parallel to the boundary line.
- For surveys that coincide with counties, show the names of adjacent counties along the
outside edge of the soil survey boundary parallel to the boundary. Where the survey joins another
state, show the adjacent state name along with the adjacent county names. Where the survey
adjoins another nation, show the national name and its provincial name along the national
boundary. If a boundary spur occurs along the map edge, show the adjacent names approximately 0.5
inch from the boundary spurs.
- For survey areas that contain more than one county or portions of counties and have county
(or state) boundaries within a survey area, show the names of counties and states as they occur
on each side of the state boundaries. Show the names more than once on maps where the boundaries
are meandering and difficult to follow.
- Position county names with approximately a 0.30-inch space between word components and
approximately 0.50-inch spacing between the county name and state name word components. Lengthen
or shorten the spacing to avoid overprinting of marginalia.
- Some maps in some states require minor civil divisions and administrative subdivisions of
counties. The following states require minor civil division boundaries and names on soil survey
maps: Connecticut, Indiana, Maine, Massachusetts, Michigan, New Hampshire, New Jersey, New York,
Ohio, Rhode Island, and Vermont.
- Show the minor civil division names widely letter spaced, horizontal in placement, and
centrally located within the bounded areas. They may be placed vertically only in areas with long
vertical dimensions. Standard type size and style is 12 point Century Schoolbook Caps.
- Where a minor civil division extends throughout the entire map, place its name near the
center, allowing clearance for other lettering and line work detail. Average spacing between
letters should be about 1.25 inches for short names and about 0.75 inch for longer names. Select
an equal spacing interval between letters, which will allow placement without overprinting.
- Where towns or cities are also minor civil divisions with different proper names, show the
official minor civil division name in letter spaced News Gothic and the place name in Spartan
Heavy. Small areas of minor civil divisions occurring on adjacent maps that can not accommodate
both the place name and the minor civil division name should show only the place name.
- If an adjoining minor civil division is the same name as the town or city minor civil
division, omit the name within the town or city minor civil division. Show only the place name
in Century Schoolbook. The exception is when the imagery of a town does not encompass the
complete minor civil division limit and large areas of open land are evident. Then show both the
minor civil division and place name.
- Administrative boundaries. Letter the names of national or state parks, forests, and
reservations in 12 point Century Schoolbook Caps. These names are usually letter spaced and placed
horizontally to neatline. Use the maximum 12 point size when the features occur over several maps. Set
their name components on separate lines and space apart to suggest the extent of their areas.
- Soil survey boundaries. Show all boundary identifications in 6 pt, Univers Condensed. Do not
show boundary identifications haphazardly on either side of the boundary line. Locate the identifications
within the area being identified in open map spaces where possible. The exception to this rule is the
limit of the soil survey boundary. Label boundaries at least one time per map and parallel to the
boundary alignment.
- If the proper name of a r
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