Map Unit Interpretation Probability

Creating maps to represent soil component interpretations or soil properties, either with a geographic information system (GIS) or with an electronic soil survey viewer, requires that each map unit delineation have a single value to display. However, soil map units commonly consist of several major and minor components, this requires decisions on how to process a map unit with multiple components. Processed components represent a portion of the total components in the map unit delineation and thus their interpretation represents only a portion of the map unit. The probability the user will encounter that interpretation can be estimated by the percent composition the interpretation occupies within the map unit.

There are potentially four common ways a user may want to process multiple component map unit interpretations.

1. Dominant component by percent.
2. Most limiting major component.
3. Least limiting major component.
4. Weighted average of major components.

Connotative color maps provide the user with the easiest to view and use interpretation maps. Implementing connotative colored interpretation maps for ranked limitation, the classic green to red for slight to severe provide a good solution. The use of probability classes provide a means to rank each limitation rating class with gradation of color intensity (light to dark) and provide the user with easy to use information about the interpretation probability of the map unit. Example how this might be implemented:

Probability   Color
Classes %     Intensity      Rating Class     Color

75 to 100      Darkest       Very Severe      Red
50 to 75         to          Severe           Pink
25 to 50         "           Moderate         Yellow
0 to 25       Lightest       Slight           Green

Map units with a 75 to 100 percent probability of severe would be the darkest pink, while map units with a 25 to 50 percent probability of severe would be nearly the lightest pink. This method would create a map, grouping interpretation ratings with the same color hue and separating their probabilities with the intensity of hue.

Examples of the four ways to process map unit interpretations follow. The user will have the ability to dynamically define the minimum percent composition of major components to be used for the interpretation. The examples use the same theoretical map unit data set, with 10 percent defined as the major component and the resulting soil interpretation map is shown.

Dominant Component by Percent

The component that makes up the largest percent composition is used to interpret the map unit delineation. The probability for the interpretation of the map unit delineation is based on the percent composition of the dominant component plus the percentage of components with the same interpretation rating.

Data:

Map unit       Component       Percent         Interpretation
Symbol         Name            Composition   value    rating class

AbA            Able            50            0.60     severe
               Beta            30            0.40     moderate
               Delta           20            0.40     moderate

AbC            Able            40            0.60     severe
               Delta           40            0.40     moderate
               Fox             15            0.60     severe
               Under           5             0.35     moderate

BdA            Beta            75            0.40     moderate
               Fox             10            0.60     severe
               Delta           10            0.40     moderate
               Able            5             0.60     severe

Map:

Interpretation Rating Classes:

Fuzzy Value          Rating Class
0.8-1.0              Very Severe
0.49-0.79            Severe
0.20-0.48            Moderate
0.0-0.19             Slight

The most limiting interpretation rating of a major component is used to interpret the map unit delineation. The probability of the interpretation for the map unit delineation is based on the percent composition of the component with the most limiting rating plus the percent composition of components with the same rating.

Data:

Map unit       Component       Percent          Interpretation
Symbol         Name            Composition   value    rating class

AbA            Able            50            0.60     severe
               Beta            30            0.40     moderate
               Delta           20            0.40     moderate

AbC            Able            40            0.60     severe
               Delta           40            0.40     moderate
               Fox             15            0.60     severe
               Under           5             0.35     moderate

BdA            Beta            75            0.40     moderate
               Fox             10            0.60     severe
               Delta           10            0.40     moderate
               Able            5             0.60     severe

Map:

Interpretation Rating Classes:

Fuzzy Value          Rating Class
0.8-1.0              Very Severe
0.49-0.79            Severe
0.20-0.48            Moderate
0.0-0.19             Slight

Least Limiting Major Component

The least limiting interpretation of a major component is used to interpret the map unit delineation. The probability for the interpretation of the map unit delineation is based on the percent composition of the component with the least limiting rating plus the percentages of components with the same rating.

Data:

Map unit       Component       Percent          Interpretation
Symbol         Name            Composition   value    rating class
AbA            Able            50            0.60     severe
               Beta            30            0.40     moderate
               Delta           20            0.40     moderate

AbC            Able            40            0.60     severe
               Delta           40            0.40     moderate
               Fox             15            0.60     severe
               Under           5             0.35     moderate

BdA            Beta            75            0.40     moderate
               Fox             10            0.60     severe
               Delta           10            0.40     moderate
               Able            5             0.60     severe

Map:

Interpretation Rating Classes:

Fuzzy Value          Rating Class
0.8-1.0              Very Severe
0.49-0.79            Severe
0.20-0.48            Moderate
0.0-0.19             Slight

Weighted Average Interpretation

Weighted average interpretation for major components is calculated based on the percent composition (on a 100 percent base) and the interpretation fuzzy value. The weighted average fuzzy value is reclassed into the appropriate rating class.

Data:

Map unit       Component       Percent   100             Interpretation
Symbol         Name            Comp.     Bases   value      Wt. Calc.   rating class
AbA            Able            50        50      0.60       0.30        severe
               Beta            30        30      0.40       0.12        moderate
               Delta           20        20      0.40       0.08        moderate
                                                 Wt.ave-    0.50        severe

AbC            Able            40        42      0.60       0.252       severe
               Delta           40        42      0.40       0.168       moderate
               Fox             15        16      0.60       0.096       severe
               Under           5                 0.35                   moderate
                                                 Wt.ave-    0.516       severe

BdA            Beta            75        79      0.40       0.316       moderate
               Fox             10        10.5    0.60       0.063       severe
               Delta           10        10.5    0.40       0.042       moderate
               Able            5                 0.60                   severe
                                                 Wt.ave-    0.421       moderate

Map:

Interpretation Rating Classes:

Fuzzy Value          Rating Class
0.8-1.0              Very Severe
0.49-0.79            Severe
0.20-0.48            Moderate
0.0-0.19             Slight