The soil delineation overlays were raster scanned at a scanning resolution of at least 0.01 inch and then converted to a vector format, or were manually digitized on a digitizing tablet with a resolution of at least 0.001 inch. Four control points corresponding to the four corners of the quadrangles were used for registration during data collection. The data sets were edge matched and merged into State coverages. A detailed edit was performed on all digital data. The topographic quadrangle units were projected into an Albers Equal Area projection and merged into statewide coverages.
Data are in preparation for Alaska.
The horizontal position of these digital data is based upon their compilation to base maps that meet National Map Accuracy Standards. The difference in positional accuracy between the map unit boundaries in the field and their digitized map locations is unknown. The locational accuracy of soil delineations on the ground varies with the transition between map units. For example, in areas where changes in soils, climate, topography, and geology occur subtly across a portion of a State, the transition between soil map unit boundaries will be gradual. Where these features change abruptly, such as from an area of foothills to a lake plain, the transition zone will be very narrow.