In those few areas where detailed maps did not exist, reconnaissance soil surveys were combined with data on geology, topography, vegetation, climate, and remote sensing images to delineate map units and estimate the percentages of components. The STATSGO map unit components are soil series phases, and their percent composition represents the estimated areal proportion of each within STATSGO map unit. The composition for a map unit is generalized to represent the statewide extent of that map unit and not the extent of any single map unit delineation. These specifications provide a nationally consistent representation of STATSGO attribute data.
The actual composition and interpretive purity of the map unit delineations were based on statistical analysis of transect data. The composition was largely determined by measuring transects on detailed soil survey maps. The number of transects used was proportional to the relative size, number, and complexity of the delineations. The combined data on the length of the map units crossed by the transects were used to determine the percentages of the different soil and nonsoil areas in each map unit.
Specific limits were established on the classification of soils and the design and name of map units. 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.
Adherence to National Cooperative Soil Survey standards and procedures is based on peer review, quality control, and quality assurance. Quality control is outlined in documents that reside with the Soil Conservation Service state soil scientist."