A copy of the USDA/SCS STATSGO Data Users Guide, which describes how to use the database is available in Adobe Acrobat and Postscript formats. The Postscipt version is divided into the following sections:
Map unit composition for a STATSGO map is determined by transecting or sampling areas on the more detailed maps and expanding the data statistically to characterize the whole map unit.
This data set consists of georeferenced digital map data and computerized attribute data. The map data are collected in 1- by 2-degree topographic quadrangle units and merged and distributed as statewide coverages. The soil map units are linked to attributes in the Map Unit Interpretations Record relational data base which gives the proportionate extent of the component soils and their properties.
A separate data set has been prepared for each U.S. state except Alaska, and for the Commonwealth of Puerto Rico. Data for the District of Columbia are included with data for Maryland. The initial generation of the data was completed in 1994.
The data format is that used by the Arc/Info GIS software package distributed by Environmental Systems Research Instiute, Inc.
STATSGO was designed primarily for regional, multicounty, river basin, State, and multistate resource planning, management, and monitoring. STATSGO data are not detailed enough to make interpretations at a county level. This soil survey product is not designed for use as a primary regulatory tool in permitting or citing decisions, but may be used as a reference source. The use of these data is not restricted and may be interpreted by organizations, agencies, units of government, or others; however, they are responsible for its appropriate application. Federal, State, or local regulatory bodies are not to reassign to the Soil Conservation Service any authority for the decisions that they make. The Soil Conservation Service will not perform any evaluations of these maps for purposes related solely to state or local regulatory programs.
When STATSGO data are overlayed with other data layers, such as land use data, caution must be used in generating statistics on the co-occurence of the land use data with the soil data. The composition of the STATSGO map unit can be characterized independently for the land use and for the soil component, but there are no data on their joint occurrence at a more detailed level. Analysis of the overlayed data should be on a map polygon basis.
Additional political, watershed, or other boundaries may be intersected with the soil data. Although the composition of each political and watershed unit may be described in terms of the STATSGO map units, information is not available to assign the components to the boundary units with full accuracy. As with the land use categories, the analysis should be restricted to the classified components.
The approximate minimum area delineated is 625 hectares (1,544 acres), which is represented on a 1:250,000-scale map by an area approximately 1 cm by 1 cm (0.4 inch by 0.4 inch). Linear delineations are not less than 0.5 cm (0.2 inch) in width. The number of delineations per 1:250,000 quadrangle typically is 100 to 200, but may range up to 400. Delineations depict the dominant soils making up the landscape. Other dissimilar soils, too small to be delineated, are present within a delineation.
Digital enlargements of these maps to scales greater than at which they were originally mapped can cause misinterpretation of the data. If enlarged, maps do not show the small areas of contrasting soils that could have been shown at a larger scale. The depicted soil boundaries, interpretations, and analysis derived from them do not eliminate the need for onsite sampling, testing, and detailed study of specific sites for intensive uses. Thus, these data and their interpretations are intended for planning purposes only.
Attribute data for some data elements may be incomplete or missing. Where data are unavailable, a mask should be used to exclude the area from analysis.
Digital data files are periodically updated. Files are dated, and users are responsible for obtaining the latest version of the data.
Logical Consistency Report: Certain node/geometry and topology (GT)-polygon/chain relationships are collected or generated to satisfy topological requirements. (The GT-polygon corresponds to the soil delineation). Some of these requirements include: chains must begin and end at nodes, chains must connect to each other at nodes, chains do not extend through nodes, left and right GT-polygons are defined for each chain element and are consistent throughout, and the chains representing the limits of the file (neatline) are free of gaps. The tests of logical consistency are performed using vendor software. The neatline is generated by connecting the explicitly entered four corners of the digital file. All data outside the enclosed region are ignored and all data crossing these geographically straight lines are clipped at the neatline. Data within a specified tolerance of the neatline are snapped to the neatline. Neatline straightening aligns the digitized edges of the digital data with the generated neatline (i.e., with the longitude/latitude lines in geographic coordinates). All internal polygons are tested for closure with vendor software and are checked on hard copy plots. All data are checked for common soil lines (i.e., adjacent polygons with the same label). Quadrangles are edge matched within the state, merged into a statewide data sets, and then edge matched to adjacent state data sets. Edge locations do not deviate from centerline to centerline by more than 0.01 inches.
Completeness Report: A map unit is a collection of areas defined and named the same in terms of their soil and/or nonsoil areas. Each map unit differs in some respect from all others in a survey area and is uniquely identified. Each individual area is a delineation. Each map unit consists of one to 21 components.
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.
Soil map unit lines and symbols were drafted in red pencil on a mylar overlay that was punch registered to fit the mylar USGS 1:250,000-scale topographic quadrangle. A detailed and complete edit was performed on all overlays before digitizing. The soil delineation overlays were raster scanned at a scanning resolution of at least 0.01 inches and converted to a vector format or were manually digitized on a digitizing tablet with a resolution of at least 0.001 inches. Four control points corresponding to the four corners of the quadrangles were used for registration during data collection. The control points were either explicitly entered or developed by the software. The data sets were edge matched and merged into statewide coverages. A detailed and complete edit was performed on all digital data.
The map unit ID uniquely identifies each closed delineation, map unit. Each map unit ID is linked to a map unit name. The map unit ID is also the key for linking information in the Map Unit Interpretations Record tables.
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 consist of the following relational tables:
The U.S. Department of Agriculture, nor any of its agencies are liable for misuse of the data. It is also not liable for damage, transmission of viruses, or computer contamination through the distribution of these data sets. The U.S. Department of Agriculture prohibits discrimination in its programs on the basis of race, color, national origin, sex, religion, age, disability, political beliefs, and marital or familial status. (Not all prohibited bases apply to all programs.)