Abstract:

This data set is a compilation of STATSGO soils, ERF1 (Version 1.2) watersheds, and County jurisdictional boundaries. The polygons of this compilation are attributed with characteristics from each of three input data sets. The details making up the remainder of this abstract are compiled from the metadata for each of the three input data sets. Citation credit belongs to the agency responsible for producing the source data set and it's associated metadata.

STATSGO DESCRIPTION:
STATSGO 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 mapunit.

The STATSGO 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.

ERF1_2 DESCRIPTION:
The digital segmented network based on watershed boundaries, ERF1_2, includes enhancements to the U.S. Environmental Protection Agency's River Reach File 1 (RF1) (USEPA, 1996; DeWald and others, 1985) to support national and regional-scale surface water-quality modeling. Alexander and others (1999) developed ERF1, which assessed the hydrologic integrity of the digital reach traces and calculated the mean water time-of-travel in river reaches and reservoirs.

ERF1_2 serves as the foundation for SPARROW (Spatially Referenced Regressions (of nutrient transport) on Watershed) modeling. Within the context of a Geographic Information System, SPARROW estimates the proportion of watersheds in the conterminous U.S. with outflow concentrations of several nutrients, including total nitrogen and total phosphorus, (Smith, R.A., Schwarz, G.E., and Alexander, R.B., 1997). This version of the network expands on ERF1 (Version 1.2; Alexander, et al., 1999) and includes the incremental and total drainage area derived from 1-kilometer (km) elevation data for North America. Previous estimates of the water time-of-travel were recomputed for reaches with water-quality monitoring sites that included two reaches. The mean flow and velocity estimates for these split reaches are based on previous estimation methods (Alexander et al., 1999) and are unchanged in ERF1_2. Drainage area calculations provide data used to estimate the contribution of a given nutrient to the outflow. Data estimates depend on the accuracy of node connectivity. Reaches split at water-quality or pesticide-monitoring sites indicate the source point for estimating the contribution and transport of nutrients and their loads throughout the watersheds.

The ERF1_2 coverage extends the earlier drainage area founded on the 1-kilometer data for North America (Verdin, 1996; Verdin and Jenson, 1996). A 1-kilometer raster grid of ERF1_2 projected to Lambert Azimuthal Equal Area, NAD 27 Datum (Snyder, 1987), was merged with the HYDRO1K flow direction data set (Verdin and Jenson, 1996) to generate a DEM-based watershed grid, ERF1_2WS_LG. The watershed boundaries are maintained in a raster (grid cell) format as well as a vector (polygon) format for subsequent model analysis.

Both the coverage, ERF1_2, and the grid, ERF1_2WS_LG, are available at: URL:http://water.usgs.gov/lookup/getspatial?erf1_2.

COUNTY JURISDICTIONAL BOUNDARIES DESCRIPTION:
The County Boundary data set portrays the state and county boundaries of the US. The data set was created by extracting county polygon features from the individual 1:2,000,000-scale County boundary Digital Line Graph (DLG) files produced by the U.S. Geological Survey. The files were then merged into a single file. The data set was last revised in 2001.

For the GeoStac Database compilation process, the STATSGO, ERF1_2, and County Boundary polygons were imported from the source file format & converted to ArcINFO polygon coverage file format, converted to a common map projection, and intersected to generate one data set made up of each of three inputs. Details surrounding the geoprocessing steps and software environments are documented in the data processing portion of this metadata document.

Purpose:

PURPOSE OF STATSGO: STATSGO depicts information about soil features on or near the surface of the Earth. These data are collected as part of the National Cooperative Soil Survey.

PURPOSE OF ERF1_2: The U.S. Environmental Protection Agency's reach file (RF1) is a database of interconnected stream segments or reaches that comprise the surface water drainage system for the United States. A variety of attributes have been assigned to each reach in support of spatial analysis and mapping applications (see USEPA, 1996; http://www.epa.gov/waters/doc/rf1_meta.html). ERF1_2 was designed to be a digital database of river reaches capable of supporting regional and national water-quality and river-flow modeling by the water-resources community. ERF1, on which ERF1_2 is based, is used at the U.S. Geological Survey to support national-level water-quality modeling with the SPARROW approach (see Alexander and others, 2000; Smith and others, 1997). In the current and earlier analyses, the reach network is used to determine flow pathways between sources of point and nonpoint pollutants (e.g., fertilizer use, municipal wastewater discharges) and downstream water-quality monitoring locations in support of predictive water-quality models of stream nutrient transport.

PURPOSE OF COUNTY BOUNDARIES: The County Boundaries data set are intended for geographic display and analysis at the national level, and for large regional areas. The data should be displayed and analyzed at scales appropriate for 1:2,000,000-scale data.

For use with the GEOSTAC Database, this data set was compiled in order to simplify presticide risk assessment and to provide a common data set upon which all stakeholders can perform analysis.

Supplemental_Information:

STATSGO SUPPLEMENTAL INFORMATION:  
The original source data set is available on an individual state basis from the following web site: http://www.essc.psu.edu/soil_info/index.cgi?soil_data&statsgo.   The Earth System Science Center in the College of Earth and Mineral Sciences at The Pennsylvania State University has compiled and updated the USDA NRCS STATSGO spatial and tabular data.

ERF1_2 SUPPLEMENTAL INFORMATION:  
The USGS generated digital segmented network based on watershed boundaries, ERF1_2, includes enhancements to the U.S. Environmental Protection Agency's River Reach File 1 (RF1) to support national and regional-scale surface water-quality modeling.  The original source data set is available from the U.S. Geological Survey at:  http://water.usgs.gov/GIS/metadata/usgswrd/XML/erf1_2.xml.

COUNTY BOUNDARIES SUPPLEMENTAL INFORMATION:
The original source data set, available at http://www.nationalatlas.gov/mld/countyp.html, provides additional details as to the compilation process of the County Boundaries of the United States.

There is a direct correlation between use constraints of this data set and the input data sets. Details on the limitations of the input data sets follow: STATSGO USE CONSTRAINTS: 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 or 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. ERF1_2 USE CONSTRAINTS: The version of RF1 used to compile ERF1_2 was an early edition of a USGS RF1 translation and was updated by USEPA (USEPA, 1996). The capabilities of the enhanced version of RF1 (ERF1_2) and the current USEPA version have not been evaluated. The user is referred to the USEPA version [URL: http://www.epa.gov/owow/monitoring/georef/history.html] for discussions of streamflow accuracy and general background on the origin of RF1. COUNTY BOUNDARIES USE CONSTRAINTS: The data are intended for geographic display and analysis at the national level, and for large regional areas. The data should be displayed and analyzed at scales appropriate for 1:2,000,000-scale data.

STATSGO DATA SET CREDIT: The U.S. Department of Agriculture, Soil Conservation Service. More information available at: http://www.essc.psu.edu/soil_info/index.cgi?soil_data&statsgo. ERF1_2 DATA SET CREDIT: U.S. Geological Survey. More information available at: http://water.usgs.gov/GIS/metadata/usgswrd/XML/erf1_2.xml COUNTY BOUNDARIES DATA SET CREDIT: National Atlas of the United States of America, The County Boundaries of the United States, 2001, generated by the USGS. More information available at: http://www.nationalatlas.gov/mld/countyp.html.

STATSGO ATTRIBUTE ACCURACY: 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. ERF1_2 ATTRIBUTE ACCURACY: The direct drainage area of each reach (RCHAREA) was computed by Smith and others (1997) using a Theissen method. It considers soley the distance to the nearest reach and does not consider any topographic features. It provides reasonably good estimates for higher-order streams, but is less accurate for lower orders. See process steps 1, 4, and 8, to assess the accuracy of MEANV and RCHTOT. COUNTY BOUNDARIES ATTRIBUTE ACCURACY: None Available.

STATSGO 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. ERF1_2 LOGICAL CONSISTENCY REPORT: This data set is believed to provide complete and accurate connectivity among the streams represented. These arcs representing streams are intended to be presented in an FNODE to TNODE orientation. The arcs are pointing in the downstream direction. COUNTY BOUNDAIRES LOGICAL CONSISTENCY REPORT: The data set was checked for topological consistency using the Arc/INFO command BUILD. No other checks for logical consistency were performed.

STATSGO 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 aras in each map unit. Specific limits were established on the classification of soils and the design and name of map units. 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. ERF1_2 COMPLETENESS REPORT: The set of streams represented reflects the choices in the U.S. Environmental Protection Agency's RF1 (DeWald and others, 1985). COUNTY BOUNDARY COMPLETENESS REPORT: The data set includes county boundaries for United States of America. Data completeness generally reflects the content of the original DLG files.

STATSGO 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 centerline to centerline by more than 0.01 inch. ERF1_2 HORIZONTAL POSITIONAL ACCURACY REPORT: Reservoir and lake boundaries were removed from the original RF1 data set. They are represented by a single trace to satisfy the connectivity requirements of the dataset. Centerlines were manually delineated within the RF1 shoreline boundaries (Alexander and others, 1999). The centerline reaches approximate the thalweg of each reservoir or lake. Shorelines of major estuaries and some coastal areas were added to the data set to serve as a stopping location for trace routines. Existing reaches extending within estuaries were deleted. COUNTY BOUNDARIES HORIZONTAL POSITIONAL ACCURACY REPORT: None Available.

For STATSGO, the original source input data set was downloaded from http://www.essc.psu.edu/soil_info/index.cgi?soil_data&statsgo, for each state in Export Exhange (.E00) file format and converted to ArcINFO Coverage. The coverages were also imported and converted into Arc Geodatabase feature class file format. The feature class and coverage files were projected to Albers Equal Area and NAD 83 datum.

For the ERF1_2 watershed boundaries, the original source data set was downloaded from from http://water.usgs.gov/GIS/metadata/usgswrd/XML/erf1_2.xml in Export Exchange (E00) and converted ArcINFO Coverage file format. The coverage was also converted and imported into Arc Geodatabase feature class file format. The feature class and coverage were both projected to Albers Equal Area and NAD 83 datum.

For County Boundaries, the original source data set was downloaded from http://www.nationalatlas.gov/mld/countyp.html and converted to both Arc Geodatabase feature class file format, and ArcINFO coverage. The feature class and coverage were projected to Albers Equal Area and NAD 83 datum.

The STATSGO / ERF1_2 intersection coverage was intersected with the County Boundaries coverage using the ArcINFO Workstation Command, IDENTIFY. This resulted in polyons extending beyond the County Boundaries to be populated with STATSGO / ERF1_2 attributes but no County Boundary attributes (including FIPS).

The ArcINFO Command, ELIMINATE, was run on the STATSGO / ERF1_2 / County Boundaries intersection coverage; where the criteria was set to: KEEPEDGE, SELECT: STATSGO ID <> W (water) & CountyBoundaryArea = 0, so that polygons missing County Boundary attributes would dissolve into adjacent polygons with the same STATSGO / ERF1_2 data and County Boundary attributes would be populated. In instances of stand-alone "islands" (populated with STATSGO / ERF1_2 attributes but not County Boundary attributes) existing beyond the input County Boundary data set (for example, instances exist along North Carolina coast line), no County Boundary data was assigned because that assignment process would be arbitrary. In addition, by Selecting out STATSGO ID's attributed by W, or Water, during the ELIMINATE Command, those STATSGO / ERF1_2 polyons extending beyond the County Boundary, and falling in water, were not included and in the process, and therefore were not assigned County Boundary attributes (this would also be an arbitrary assignment process). The resultant data set contains islands and polygons falling in water that extend beyond the input County Boundaries data set populated by STATSGO / EFR1_2 data but not County Boundary data.

statsgo_erf1v2ws_county_intrsct

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