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 soil survey
area and edge locations generally do not deviate from centerline to
centerline by more than 0.01 inch.
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 or more components.
Soil scientists identify small areas of soils or nonsoil areas
(special soil features) that have properties and behavior
significantly different than the named soils in the surrounding map
unit. Other inclusions that have a minimal effect on use and
management, or those that could not be precisely located, were not
mapped.
Specific limits were established on the classification of soils,
design and name of map units, location of special soil features,
and the percentages of allowable inclusions. 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. Handb. 18.
The actual composition and interpretive purity of the map unit
delineations were based on statistical analysis of field
observations and transect data. Adherence to National Cooperative
Soil Survey standards and procedures is based on peer review,
quality control, and quality assurance. Quality control is outlined
in the memorandum of understanding for the soil survey area and in
documents that reside with the Natural Resources Conservation
Service state soil scientist. Four kinds of map units are used in
soil surveys: consociations, complexes, associations, and
undifferentiated groups.
Consociations - Consociations are named for the dominant soil. In
a consociation, delineated areas are dominated by a single soil
taxon and similar soils. At least one half of the pedons in each
delineation are of the same soil component so similar to the
named soil that major interpretations are not affected
significantly. The total amount of dissimilar inclusions of
other components in a map unit generally does not exceed about
15 percent if limiting and 25 percent if nonlimiting. A single
component of a dissimilar limiting inclusion generally does not
exceed 10 percent if very contrasting.
Complexes and associations - Complexes and associations are named
for two or more dissimilar components with the dominant
component listed first. They occur in a regularly repeating
pattern. The major components of a complex cannot be mapped
separately at a scale of about 1:24,000. The major components of
an association can be separated at a scale of about 1:24,000. In
each delineation of either a complex or an association, each
major component is normally present, though their proportions
may vary appreciably from one delineation to another. The total
amount of inclusions in a map unit that are dissimilar to any of
the major components does not exceed 15 percent if limiting and
25 percent if nonlimiting. A single kind of dissimilar limiting
inclusion usually does not exceed 10 percent.
Undifferentiated Groups - Undifferentiated groups consist of two
or more components that do not always occur together in the same
delineation, but are included in the same named map unit because
use and management are the same or similar for common uses.
Every delineation has at least one of the major components and
some may have all of them. The same principles regarding
proportion of inclusions apply to undifferentiated groups as to
consociations.
Minimum documentation consists of three complete soil profile
descriptions that are collected for each soil added to the legend,
one additional per 3,000 acres mapped; three 10 observation
transects for each map unit, one additional 10 point transect per
3,000 acres.
A defined standard or level of confidence in the interpretive
purity of the map unit delineations is attained by adjusting the
kind and intensity of field investigations. Field investigations
and data collection are carried out in sufficient detail to name
map units and to identify accurately and consistently areas of
about 4 acres.