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."
Process Step
Process Description: 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. Source
Used Citation Abbreviation: USGS1, SCS3
Process Date: 1994"
Attribute Accuracy
Attribute Accuracy Report: Attribute accuracy is tested by manual
comparison of the source with hard copy plots and/or
symbolized display of the map data on an interactive computer graphic
system. Selected attributes that cannot be visually
verified on plots or on screen are interactively queried and verified
on screen. In addition, the attributes are tested
against a master set of valid attributes. All attribute data conform
to the attribute codes in the signed classification and correlation
document and amendments and are current as of the date of digitizing.
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.
Positional Accuracy
Horizontal Positional Accuracy
Horizontal Positional Accuracy Report: The accuracy 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 acuracy 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 will be
very narrow. Soil delineation boundaries were
digitized within 0.01 inches of their locations on the digitizing
source. The digital map elements are edge
matched between data sets. The data along each state boundary are
matched against the data for the adjacent
state. Edge locations generally do not deviate from centerline to
centerline by more than 0.01 inch."
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.
U.S. Department of Agriculture. 1993. Soil Survey Manual. Soil Surv. Staff, U.S. Dep. Agric. Handbook 18.
U.S. Department of Agriculture. 1993. National Soil Survey Handbook, title 430-VI. Soil Surv. Staff, Soil Conserv. Serv.
U.S. Department of Agriculture. 1994. State Soil Geographic (STATSGO) Data Base: Data use information. Soil Conserv. Serv.
U.S. Department of Agriculture. State Soil Survey Database Data Dictionary. Soil Conserv. Serv."