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Soil Survey Manual - Table 2-1

Key for Identifying Kinds of Soil Surveys

Level of data needed Field procedures Minimum-size delineation (hectares)1 Typical components of map units2 Kind of map units Appropriate scales for field mapping and publications
1st order - Very intensive (i.e., experimental plots or individual building sites.) The soils in each delineation are identified by transecting or traversing. Soil boundaries are observed throughout their length. Remotely sensed data are used as an aid in boundary delineation. 1 or less Phases of soil series, miscellaneous areas. Mostly consociations, some complexes, miscellaneous areas. 1:15,840 or larger
2nd order - Intensive (e.g. general agriculture, urban planning.) The soils in each delineation are identifies by field observations and by remotely sensed data. Boundaries are verified at closely spaced intervals. 0.6 to 4 Phases of soil series, miscellaneous areas, few named at a level above the series. Consociations, complexes; few associations and undifferentiated groups. 1:12,000 to 1:31,680
3rd order - Extensive (i.e., range or community planning.) Soil boundaries plotted by observation and interpretation of remotely sensed data. Soil boundaries are verified by traversing representative areas and by some transects. 1.6 to 16 Phases of soil series or taxa above the series; or miscellaneous areas. Mostly associations or complexes, some consociations and undifferentiated groups. 1:20,000 to 1:63,360
4th order - Extensive (e.g., general soil information for broad statements concerning land-use potential and general land management.) Soil boundaries plotted by interpretation of remotely sensed data. Boundaries are verified by traversing representative areas and by some transects. 16 to 252 Phases of soil series or taxa above the series or miscellaneous areas. Mostly associations; some complexes, consociations and undifferentiated groups. 1:63,360 to 1:250,000
5th order - Very extensive (e.g., regional planning, selections of areas for more intensive study.) The soil patterns and composition of map units are determined by mapping representative ideas and like areas by interpretation of remotely sensed data. Soils verified by occasional onsite investigation or by traversing. 252 to 4,000 Phases of levels above the series, miscellaneous areas. Associations; some consociations and undifferentiated groups. 1:250,000 to 1:1,000,000 or smaller

1.This is about the smallest delineation allowable for readable soil maps (see Table 2-2). In practice, the minimum-size delineations are generally larger than the minimum-size shown.
2.Where applicable, all kinds of map units (consociations, complex, associations, undifferentiated) can be used in any order of soil survey.