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
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
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
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)
DATA CONTENT AND FORMAT
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
NRCS's attribute data for
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,
State Soil Scientist
2118 W. Park Court
Champaign, IL 61821
Resource Inventory Specialist
2118 W. Park Court
Champaign, IL 61821