Specific limits were established on the classification of soils, design and name of map units, location of special soil features, and the percentages of allowable inclusions. These limits are outlined in U.S. Department of Agriculture. 1975. Soil Taxonomy: A basic system of soil classification for making and interpreting soil surveys. Soil Conserv. Serv., U.S. Dep. Agric. Handb. 436.; U.S. Department of Agriculture. 1992. Keys to Soil Taxonomy. SMSS Technical Monograph No. 19. Soil Surv. Staff, Soil Conserv. Serv.; U.S. Department of Agriculture. 1993. National Soil Survey Handbook, title 430- VI. Soil Surv. Staff, Soil Conserv. Serv.; and U.S. Department of Agriculture. 1993. Soil Survey Manual. Soil Surv. Staff, U.S. Dep. Agric. Handbook 18.
The actual composition and interpretive purity of the map unit delineations were based on statistical analysis of field observations and transect data. Adherence to National Cooperative Soil Survey standards and procedures is based on peer review, quality control, and quality assurance. Quality control is outlined in the memorandum of understanding for the soil survey area and in documents that reside with the Natural Resources Conservation Service state soil scientist. Four kinds of map units are used in soil surveys: consociations, complexes, associations, and undifferentiated groups.
Consociations - Consociations are named for the dominant soil. In a consociation, delineated areas are dominated by a single soil taxon and similar soils. At least one half of the pedons in each delineation are of the same soil components so similar to the named soil that major interpretations are not affected significantly. The total amount of a dissimilar inclusions of other components in a map unit generally does not exceed about 15 percent if limiting and 25 percent if nonlimiting. A single component of dissimilar limiting inclusion generally does not exceed 10 percent if very contrasting.
Complexes and associations - Complexes and associations are named for two or more dissimilar components with the dominant component listed first. They occur in a regularly repeating pattern. The major components of a complex cannot be mapped separately at a scale of about 1:15,840 (the scale at which the county was mapped at) major components of an association can be separated at a scale of about 1:15,840. In each delineation of either a complex or an association, each major component is normally present, though their proportions may vary appreciably from one delineation to another. The total amount of inclusions in a map unit that are dissimilar to any of the major components does not exceed 15 percent if limiting and 25 percent if nonlimiting. A single kind of dissimilar limiting inclusion usually does not exceed 10 percent.
Undifferentiated Groups - Undifferentiated groups consist of two or more components that do not always occur together in the same delineation, but are included in the same named map unit because use and management are the same or similar for common uses. Every delineation has at least one of the major components and some may have all of them. The same principles regarding proportion of inclusions apply to undifferentiated groups as to consociations.
Minimum documentation consists of three complete soil profile descriptions that are collected for each soil added to the legend, and one to three 10 observation transects for each map unit.
A defined standard or level of confidence in the interpretive purity of the map unit delineations is attained by adjusting the kind and intensity of field investigations. Field investigations and data collection are carried out in sufficient detail to name map units and to identify accurately and consistently areas of about 5 acres.
Map Unit Delineations are described by the Map Unit Interpretations Record data base. This attribute data base gives the proportionate extent of the component soils and the properties for each soil. The data base contains both estimated and measured data on the physical and chemical soil properties and soil interpretations for engineering, water management, recreation, agronomic, woodland, range, and wildlife uses of the soil. The soil Map Unit Interpretations Record data base consists of the following relational tables: codes (data base codes) - stores information on all codes used in the data base comp (map unit component) - stores information for soil map components compyld (component crop yield) - stores crop yield information for soil map unit components forest (forest understory) - stores information for plant cover as forest understory for soil map unit components helclass (highly erodible lands class) - stores the highly erodible land classification for wind and water assigned to the soil map units. Table not populated. hydcomp (hydric component information) - stores data related to the hydric classification, criteria, landform, etc. inclusn (map unit inclusion) - stores the names of soils included in the soil map units interp (interpretation) - stores soil interpretation ratings (both limitation ratings and suitability ratings) for soil map unit components layer (soil layer) - stores characteristics of soil layers for soil map unit components mapunit (map unit) - stores information that applies to all components of a soil map unit mucoacre (map unit county acres) - stores the number of acres for the map unit within a county muyld (map unit yield) - stores crop yield information for the soil map unit plantcom (plant composition) - stores plant symbols and percent of plant composition associated with components of a soil map unit. Table not populated. plantnm (plant name) - stores the common and scientific names for plants used in the data base rangenm (range name) - stores the range site names. Table not populated. rsprod (range site production) - stores range site production information for soil map unit components. Table not populated. ssacoac (soil survey area county acreage) - stores the acreage for the county within the boundary of the soil survey area ssarea (soil survey area) - stores information that will apply to an entire soil survey area taxclass (taxonomic classification) - stores the taxonomic classification for soils in the data base windbrk (windbreak) - stores information on recommended windbreak plants for soil map unit components wlhabit (wildlife habitat) - stores wildlife habitat information for soil map unit components woodland (woodland) - stores information on common indicator trees for soil map unit components woodmgt (woodland management) - stores woodland management information for soil map unit components yldunits (yield units) - stores crop names and the units used to measure yield
Special features are described in the feature table. It includes a feature label, feature name, and feature definition for each special ad hoc feature in the survey area.
U.S. Department of Agriculture. 1993. National Soil Survey Handbook, title 430-VI. Soil Surv. Staff, Soil Conserv. Serv.
U.S. Department of Agriculture. 1993. Soil Survey Manual. Soil Surv. Staff, U.S. Dep. Agric. Handbook 18.
U.S. Department of Agriculture. 1994. Soil Survey Geographic (SSURGO) Data Base: Data use information. Soil Conserv. Serv.
U.S. Department of Agriculture. State Soil Survey Database Data Dictionary. Soil Conserv. Serv.