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Digital Soils Data Fact Sheet

DIGITAL SOILS DATA FACT SHEET

U.S. Department of Agriculture
Natural Resources Conservation Service

DIGITAL SOILS DATA

1:12,000 to 1:7,500,000-Scale Digital Soils Information from the SSURGO, STATSGO, and NATSGO Data Bases


The Natural Resources Conservation Service (NRCS) has the federal responsibility for the National Cooperative Soil Survey (NCSS) and federal leadership for collecting, storing, maintaining, and distributing soils information of privately owned lands in the United States. The Federal Geographic Data Committee and the Office of Management and Budget have formally assigned the responsibility for national coordination of digital soils data to the NRCS.

As a step toward making digital soil data available, the NRCS is releasing for sale, boundary and attribute data from it's major soil data bases.

NRCS has established three digital soil geographic data bases representing different intensities of soil mapping. Common to each soil geographic (spatial) data base is the linkage to a soil interpretations (attribute) record data base, which gives the proportionate extent of the component soils and their properties for each map unit.

With these digital data bases, users can store, retrieve, analyze, and display soil data in a highly efficient manner, as well as integrate the data with other spatially referenced resource and demographic data in a Geographic Information System (GIS).


THE THREE DATA BASES

The three soil geographic data bases are the Soil Survey Geographic Data Base (SSURGO), the State Soil Geographic Data Base (STATSGO), and the National Soil Geographic Data Base (NATSGO). Components of map units in each geographic data base are generally phases of soil series. Phases of series enable the most precise interpretation. Interpretations are displayed differently for each geographic data base to be consistent with the level of detail mapped. The soil interpretations record data base encompasses more than 25 soil physical and chemical properties for approximately 18,000 soil series recognized in the United States.

Information such as particle size distribution, bulk density, available water capacity, soil reaction, salinity, and organic matter is included for each major layer of the soil profile. Also included are data on flooding, water table, bedrock, subsidence characteristics of the soil, and interpretations for erosion potential, septic tank limitations, engineering, building and recreation development, and cropland, woodland, wildlife habitat, and rangeland management.

SSURGO, the most detailed level of information, is used primarily for farm and ranch conservation planning; range and timber management; and county, township, and watershed resource planning and management. Utilizing the soil attributes, this data also serves as an excellent source to review site development proposals and land use potential, make land use assessments and to identify potential wetland areas.

Using national mapping standards, soil maps in the SSURGO data base are made by field methods, using observations along soil delineation boundaries and traverses, and determining map unit composition by field transects. Aerial photographs are interpreted and used as the field map base. Maps are made at scales ranging from 1:12,000 to 1:31,680 and incorporated with comprehensive descriptions to produce the NCSS publications.

Digitizing is by line segment (vector) in accordance with NRCS-established digitizing specifications and standards for duplicating the original soil survey map. The mapping bases are normally orthophotoquads or 7.5 minute topoquads. Digitizing is done by NRCS or by cooperating state and local governments.

SSURGO data are collected and archived in 7.5 minute topographic quadrangle units, and distributed as complete coverage for a soil survey area usually consisting of ten or more quadrangle units. The adjoining 7.5 minute units are matched within the survey areas.

STATSGO is used primarily for river basin, state, and multicounty resource planning, management, and monitoring.

Soil maps for STATSGO were made by generalizing the detailed soil survey maps. Where more detailed maps are not available, data on geology, topography, vegetation, and climate were assembled, together with satellite images. Soils of analogous areas are studied, and a determination of the classification and extent of the soils is made.

Map unit composition for STATSGO is determined by transecting or sampling areas on the detailed maps and expanding the data statistically to characterize the whole map unit.

STATSGO was mapped on the U.S. Geological Survey's 1:250,000-scale topographic quadrangle series. Soil boundaries were digitized by line segment (vector) to comply with national guidelines and standards.

STATSGO data are archived and distributed as complete coverage for a state. STATSGO data are joined between states.

The NATSGO Data Base

NATSGO is used primarily for national, regional, and multistate resource appraisal, planning, and monitoring, and is under development.

The boundaries of the major land resource area (MLRA) and land resource regions are included as part of the 1992 Natural Resources Inventory (NRI) Database.

DATA CONTENT AND FORMAT

Spatial Data

SSURGO, STATSGO, and NATSGO spatial data are distributed to the public from the National Cartography and GIS Center (NCG) in the USGS Digital Line Graph (DLG-3) Optional Distribution Format.

SSURGO data are archived in various formats. Depending on the format requested, the customer's request may be delayed to reformat the data to the DLG-3 Optional format. NRCS soil map symbols (AbC) are not normally carried within the DLG-3 Optional format. However, these map symbols are made available as a unique ASCII file when NRCS soils data are distributed in the DLG format.

The distribution medium for spatial data will normally be CD-ROM-ISO9660 format, but may be cartridge tape, also by mutual agreement.

Additional information regarding file formats for data, as well as the technical specifications for digitizing NRCS soils data, is available from the NCG.

Attribute Data

NRCS's attribute data for SSURGO and STATSGO are stored in a relational data base. This format is a nonfixed length, tab delimited, ASCII file. NATSGO is stored in a flat ASCII file. Attribute data are distributed as part of each complete dataset.


Before obtaining digital soil data, the user needs to identify the area of interest and examine the anticipated use of the data. More importantly, the user should be knowledgeable of the software and/or data format capabilities available on the computer system intended for use. The user should be knowledgeable of soils data and their characteristics. If you need assistance, contact:

Ron Collman 
Acting State Soil Scientist
USDA-NRCS
2118 W. Park Court
Champaign, IL 61821
217-353-6639
E-mail: Ron.Collman@il.nrcs.usda.gov

or

Tim Prescott
Resource Inventory Specialist
USDA-NRCS
2118 W. Park Court
Champaign, IL 61821
217-353-6637
E-mail:tim.prescott@il.usda.gov