This data set is a digital general soil association map developed by the National Cooperative Soil Survey. It consists of a broad based inventory of soils and nonsoil areas that occur in a repeatable pattern on the landscape and that can be cartographically shown at the scale mapped. The soil maps for STATSGO are compiled by generalizing more detailed soil survey maps. Where more detailed soil survey maps are not available, data on geology, topography, vegetation, and climate are assembled, together with Land Remote Sensing Satellite (LANDSAT) images. Soils of like areas are studied, and the probable classification and extent of the soils are determined.
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.
These spatial data are distributed in support of the CDSS project.
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.
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.
1) Related the polygon attribute table to the table comp.dbf using the MUID field. The records where the COMPNAME field has a value of "ROCK OUTCROP" or "RUBBLE LAND" were excluded from the analysis.
2) The layer.dbf table was related to the table compyld.dbf using the MUIDSEQNUM field, which is a subset of the MUID values (i.e.: one MUID can have many MUIDSEQNUM values). The compyld.dbf table describes the crops that are cultivated on that soil. Records in layer.dbf that did not relate to a record in the compyld.dbf table (and therefore are not cultivated) were excluded from the study.
3) Because some records were excluded from the analysis (steps 1 & 2), there are cases where the percentage values in the comp.dbf table's COMPPCT field no longer sum to 100 percent for each MUID. A sum of the COMPPCT field was calculated for each unique MUID value from the remaining records. This sum was used to create an adjusted percentage value (the COMPPCT field divided by this sum).
4) Three depth categories, named 0-12", 12- 24", and 24-60" were created. The fields LAYDEPL and LAYDEPH in the layer.dbf table define the low and high depth values (respectively) for a soil. A record in the layer.dbf table was classified as belonging to a depth category if it met the following criteria:
0-12" layer: If laydepl <= 8 inches.
12-24" layer: If laydepl <= 18 and laydeph >= 18 inches.
24-60" layer: If laydepl < 60 and laydeph > 30 inches.
The average of the AWCL and AWCH fields in the layer.dbf table was calculated for each of the three depth categories for each record. Note that a record that does not fall into a depth category will have a NULL value for the average AWC for that depth category. This is important because NULL values are not used in further calculations.
5) The average of the average AWC values (from step 4) was calculated in each depth category for each unique MUIDSEQNUM value. Note that these averages only use non-NULL values from step 4, so that records not in a depth category are not counted in the calculations.
6) The averages from step 5 were multiplied by the adjusted COMPPCT values (from step 3) to create a weighted AWC value for each depth category for each MUIDSEQNUM.
7) The values from step 6 were summed for each unique MUID in each of the three depth categories.
8) The three depth categories are 12, 12, and 36 inches deep, respectively, and thus the categories represent 20, 20, and 60 percent of the first 60 inches of soil. The weighted AWC average for each unique MUID was calculated by multiplying the weighted AWC value for each depth category (from step 7) by that depth category's percent of the the first 60 inches of soil, and summing these three products.
9) Only the cultivated MUIDSEQNUM records were used to calculate the AWC. For this reason, a polygon whose MUID has no cultivated MUIDSEQNUM records will have no AWC value associated with it. Steps 1-8 were repeated, skipping step 2, to create AWC values derived from all the MUIDSEQNUM records.
10) The weighted AWC values for the cultivated soils only (from step 8) were added to the polygon attribute table in the field "AWC". The records that were updated with these values contain a value of 2 in the field "AWC-CATEGORY".
11) The records that still contained no AWC value were given the AWC value calculated using all the MUIDSEQNUM records (from step 9). These records were given a value of 1 in the field "AWC-CATEGORY".
12) The records that still contained no AWC value were given a value of 0 in the field "AWC-CATEGORY". These records mostly relate to excluded polygons (step 1) or polygons with no valid AWC values (mostly water body polygons).
12) The MUNAME field from the mapunit.dbf table (the names of the soil types in that MUID) was added to the polygon attribute table.
Projection ALBERS Zunits NO Units METERS Spheroid CLARKE1866 Xshift 0.0000000000 Yshift 0.0000000000 Parameters 29 30 0.000 /* 1st standard parallel 45 30 0.000 /* 2nd standard parallel -96 0 0.000 /* central meridian 23 0 0.000 /* latitude of projection's origin 0.00000 /* false easting (meters) 0.00000 /* false northing (meters)
2) Clipped coverage for the State of Colorado to the DWR Division boundary.
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: codes (data base codes) - stores information on all codes used in the data base comp (map unit component) - stores information which will apply to a specific component of a soil map unit compyld (component crop yield) - stores crop yield information for soil map unit components forest (forest understory) - stores information for plant cover as forest understory for soil map unit components interp (interpretation) - stores soil interpretation ratings (both limitation ratings and suitability ratings) to soil map unit components layer (soil layer) - stores characteristics which apply to soil layers for soil map unit components mapunit (map unit) - stores information which applies to all components of a soil map unit plantcom (plant composition) - stores plant symbols and percent of plant composition associated with components of soil map units plantnm (plant name) - stores the common and scientific names for plants used in the data base rsprod (range site production) - stores range site production information for soil map unit components taxclass (taxonomic classification) - stores the taxonomic classification for soils in the data base windbrk (windbreak) - stores information on recommended windbreak plants for soil map unit components wlhabit (wildlife habitat) - stores wildlife habitat information for soil map unit components woodland (woodland) - store information on common indicator trees for soil map unit components woodmgt (woodland management) - stores woodland management information for soil map unit components yldunits (yield units) - stores crop names and the units used to measure yield
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.)