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Spatial Data in Geographic Information System Format on Agricultural Chemical Use, Land Use, and Cropping Practices in the United States

By William A. Battaglin and Donald A. Goolsby

This is an electronic version of U.S. Geological Survey Water-Resources Investigations Report 94-4176. To view the figures, you will need an external viewer for ".gif" images. To see the tables, you will need a PostScript viewer.

The original report contains examples of data documentation, and instructions for ordering the data. This version includes direct links for on-line viewing of the actual documentation and for on-line retrieval of the data sets.

Table of Contents

ABSTRACT

The spatial data in geographic information system format described in this report consist of estimates for all counties in the conterminous United States of the annual use of 96 herbicides in 1989; annual sales of nitrogen fertilizer, in tons, for 1985-91; and agricultural expenses, land use, chemical use, livestock holdings, and cropping practices in 1987. The source information, originally in tabular form, is summarized as digital polygon attribute data in the 18 geographic information system spatial data layers (coverages) provided. The information in these coverages can be used in estimating regional agricultural-chemical use or agricultural practices and in producing visual displays and mapping relative rates of agricultural-chemical use or agricultural practices across broad regions of the United States.

INTRODUCTION

Agricultural chemicals (herbicides, insecticides, and fertilizers) are used extensively in the United States to increase yields of agricultural crops. Many agricultural chemicals are partially water soluble and can leach to ground water or run off to surface water (Thurman and others, 1992). The presence of agricultural chemicals in ground water and surface water has been documented in many recent reports (Madison and Brunett, 1985; Goolsby and others, 1991a; Goolsby and others, 1991b; Goolsby and Battaglin, 1993; Spalding and Exner, 1991; Thurman and others, 1991; Thurman and others, 1992; U.S. Environmental Protection Agency, 1992; Battaglin and others, 1993; Scribner and others, 1993; Kolpin and others, 1993; and Burkart and Kolpin, 1993). Analysis of relations among the presence and distribution of agricultural chemicals in the environment, estimates of agricultural-chemical use, estimates of agricultural land use, and descriptions of hydrologic conditions is greatly facilitated by the application of geographic- information-system (GIS) technology (Battaglin and others, 1994; Battaglin and others, 1993; Goolsby and Battaglin, 1993; Kolpin and others, 1993; Rains and Latham, 1993; and He and others, 1993).

This report describes the data sources and methods used to construct spatial data layers in GIS format (coverages) on agricultural-chemical use and agricultural practices that may help in future research concerning the presence and distribution of agricultural chemicals in water resources of the United States. The coverages contain information at the county scale for the conterminous United States. The 3,111 counties of the conterminous United States constitute the study area for this report.

SCOPE

The report contains: (1) 18 ARC/INFO (GIS software produced and distributed by Environmental Systems Research Institute) GIS coverages summarizing the annual use of 96 herbicides in 1989; annual sales of nitrogen fertilizer, in tons, for 1985-91; and agricultural expenses, land use, chemical use, livestock holdings, and cropping practices in 1987, for counties in the conterminous United States; (2) complete on-line documentation of the 18 coverages and a self-installing version the U.S. Geological Survey's documentation AML (ARC Macro Language) (Nebert, 1994); and (3) 12 page-sized color maps summarizing selected attribute data from the 18 coverages (see figs. 1-12). These products were prepared by the U.S. Geological Survey in cooperation with the U.S. Environmental Protection Agency under Interagency Agreement DW14934820-01-1.

Information from four primary sources is summarized as polygon attribute data in the 18 coverages provided. Five coverages summarizing the use of 96 herbicides were constructed from estimates reported in Gianessi and Puffer (1991). Seven coverages summarizing annual nitrogen fertilizer sales, in tons, for the years 1985-91 were constructed from estimates reported by the U. S. Environmental Protection Agency (1990) and by Jerald Fletcher (West Virginia University, written commun., 1992). Six coverages summarizing agricultural expenses, land use, chemical use, livestock holdings, and cropping practices were constructed from estimates reported by the U. S. Department of Commerce (1989a, 1989b) in the 1987 Census of Agriculture. The 18 coverages contain a total of 521 attributes that were derived from the four cited data sources. All coverages described in this report were created and documented, and are stored on-line, in accordance with the guidelines given by Nebert (1994).

METHODS USED TO PROCESS SOURCE DATA INTO GEOGRAPHIC INFORMATION SYSTEM PRODUCTS

A polygon coverage representing county boundaries in the conterminous United States, as well as lakes, estuaries, and other nonland-area features, is used as the base for the coverages described in this report. The base county coverage was derived from the Digital Line Graph (DLG) files representing the 1:2,000,000-scale map in the National Atlas of the United States (U.S. Geological Survey, 1970; Domeratz and others, 1983). Polygon coverages in general are used to represent area features. Polygons are defined by a series of arcs that form a many-sided, closed figure. A label point inside each polygon is used to assign attributes to the polygon. Attributes can contain any information that pertains to the area represented by the polygon. For example, every polygon in the base coverage contains an attribute called PLYTYPE which is a numeric code that indicates whether the polygon represents land, a lake, or an estuary. Each county land polygon is identified by a five-digit Federal Information Processing Standard (FIPS) code. Some counties are represented by more than one polygon.

A missing value code of -99.0 is used when no attribute data are given for a county land polygon and also is used for all nonland-area polygons. Attribute values in counties represented by one polygon are equal to county totals. For counties described by more than one polygon, attribute values are provided for each polygon and are calculated as the county total multiplied by the ratio of the area of each county polygon to the total area of the county. For example, if county A is represented by two polygons of equal area, and 1,000 pounds of atrazine are reported to have been used in county A, then the value of the attribute for pounds of atrazine used for each of the two polygons representing county A would be 500 pounds.

Construction of Geographic Information System Coverages

Automated procedures were developed for processing the raw herbicide-use, nitrogen-fertilizer- sales, and 1987 Census of Agriculture data into ARC/ INFO coverage attributes. Procedures generally were coded in AML (Environmental Systems Research Institute, 1992); however, some Fortran codes and awk programs (Aho and others, 1988) also were used. The procedure was to copy the ARC/INFO county base coverage to a new coverage and then execute an attribute addition AML program to transfer attribute values from the raw data files to the new coverage. Other automated procedures were developed to calculate summary statistics of attribute values, and to produce maps (color postscript files) that represent attribute values across the United States (figs. 1-12). The on-line documentation file that accompanies each coverage was generated by using the program document.aml, which is available from the U.S. Geological Survey (Nebert, 1994). On-line data documentation may be seen by following the instructions in appendix 1.

All products were inspected visually for obvious errors. County-level herbicide-use estimates were sometimes absent as a result of withheld census data. County herbicide-use data cannot be totaled to obtain the State use totals reported in Gianessi and Puffer (1991) because of differences between statewide crop-acreage estimates (which include all counties) and county-level crop-acreage estimates (some of which are withheld because of census disclosure rules). Estimates of nitrogen-fertilizer use in Utah in 1985 are missing. Estimates from the 1987 Census of Agriculture were compared visually with maps published in U. S. Department of Commerce (1990). Most missing data in unexpected areas results from withholding of Census of Agriculture data as a result of census disclosure rules. Additional details concerning the processing of coverage and ancillary information are given in the Data Sources For Geographic Information System Coverages section of this report.

Construction of Color Maps

Color maps summarizing 24 selected attributes from the 18 coverages were constructed in ARC/INFO by use of a consistent methodology (see figs. 1-12). The maps were developed to show locations and relative rates of agricultural-chemical use or agricultural practices across broad regions of the United States. A statistical distribution was used to select six class intervals for the graphic display of agricultural-chemical use, land use, and cropping- practice data. The empty (white) class (see figs. 1-12) represents counties in which attribute values are missing or zero. The first shaded class (light blue) represents attribute values that are reported (not missing or zero) and as large as the 25th percentile of the data. The second shaded class (green) represents attribute values that are greater than the 25th percentile and as large as the 50th percentile (median) of the data. The third shaded class (yellow) represents attribute values that are greater than the median and as large as the 75th percentile of the data. The fourth shaded class (orange) represents attribute values that are greater than the 75th percentile and as large as the 75th percentile plus two standard deviations of the data. The fifth shaded class (red) represents attribute values that are greater than the 75th percentile plus two standard deviations.

DATA SOURCES FOR GEOGRAPHIC INFORMATION SYSTEM COVERAGES

Herbicide-Use Data

Five coverages summarizing the use of 96 herbicides were constructed from estimates reported in Gianessi and Puffer (1991). A ranking of national herbicide-use amounts (Gianessi and Puffer, 1991, Table A-6) was used to divide herbicide-use attribute data into five coverages. The tabular estimates of herbicide use by county and by crop were constructed by Gianessi and Puffer (1991) by:

(1) compiling statistics, by State and by crop, on the percentage of acres treated with a given herbicide and the average annual application rate of the herbicide from responses to surveys sent to U.S. Department of Agricultural Cooperative Extension Service weed scientists in 1987 and 1989;
(2) augmenting survey data with published surveys and reports from individual States (U.S. Department of Agriculture, 1989a; U.S. Department of Agriculture, 1989b; Rinehold and Witt, 1989)
(3) establishing herbicide-use profiles, by State and by crop, that contain the percentage of acres treated and average annual application rates;
(4) multiplying county-level crop-acreage estimates from the 1987 Census of Agriculture (U.S. Department of Commerce, 1989a) by the percentage of acres treated and the average annual application rates to obtain herbicide-use estimates; and
(5) tabulating herbicide-use amounts and acres treated by crop and by county.

Eighty-four crops were profiled, resulting in usage estimates for 96 herbicide active ingredients. Although crop acreages are from 1987 data, the herbicide-use estimates generally reflect 1989 usage amounts (Gianessi and Puffer, 1991). Estimates of herbicide use by county were generated from a combination of data collected from surveys of weed scientists and from surveys of farmers. Herbicide-use profile data were generated by using ancillary data sources or were calculated from profiles for neighboring States when no responses to surveys or published reports were available (Gianessi and Puffer, 1991). Sampling and statistics were used to account for crop acreages from nonresponding farm operations. Thus, the information describing crop acreages is subject to sampling variability as well as reporting and coverage errors (U.S. Department of Commerce, 1989b). Census disclosure rules also prevent the publication of information that would reveal the operation of individual farms.

Herbicide-use attributes by crop and by county were extracted from the tabular data files provided by Gianessi and Puffer (1991). The total use of each herbicide on all crops was calculated for all counties with herbicide use. Three attributes were added to an ARC/INFO coverage for each of the 96 herbicides. Attributes with names ending in .ACR are estimates of the number of acres treated with a given herbicide. Attributes with names ending in .LBS are estimates of the total number of pounds of active ingredient of a given herbicide applied on all crops. Attributes ending in .USE are estimates of a county-level herbicide-use rate in pounds per square mile. Attribute names are keyed to four-digit herbicide code numbers provided in table 1. For example, estimates of the number of pounds of atrazine applied are contained in the attribute named H1980.LBS. Herbicide-coverage names, attribute names, and the crops on which the largest amount of active ingredient of each herbicide was used are listed in table 2.

Herbicide-use estimates for counties represented by one polygon are equal to county totals. For counties described by more than one polygon, herbicide-use estimates are provided for each polygon and are calculated as the county total multiplied by the ratio of the area of the county polygon divided by the total area of the county. A missing-value code of -99.0 is used when no herbicide-use estimates are available for a county and for all nonland-area polygons. A missing-value code in a county land polygon can indicate any of the following conditions:

-- herbicide not used in the county (for example, no alachlor used in county),
-- crop data withheld because of census disclosure rules,
-- crop data not available to the census, or
-- crop data not published because county contains fewer than 10 farms.

Nitrogen-Fertilizer Sales Data

Seven coverages summarizing annual nitrogen-fertilizer sales, in tons, for the fertilizer years 1985-91 (for example, the 1987 fertilizer year is the period from July 1, 1986, to June 30, 1987), were constructed from estimates reported by the U.S Environmental Protection Agency (1990). Estimates for 1990 and 1991 were provided to the U.S. Geological Survey by Jerald Fletcher (West Virginia University, written commun., 1992) in cooperation with the National Fertilizer and Environmental Research Center, Tennessee Valley Authority (TVA). Estimates of fertilizer sales estimates were generated and are reported as tons of actual nutrient (inorganic nitrogen, phosphate, and potash). The fertilizer-sales estimates do not account for the use of manure.

The method used to construct fertilizer sales estimates is similar to that used by Alexander and Smith (1990). The data are summarized for fertilizer years . The county-level nitrogen-fertilizer sales estimates (U.S. Environmental Protection Agency, 1990) were constructed by:

(1) compiling annual State fertilizer-sales data reported as tonnages to the National Fertilizer and Environmental Research Center of the TVA;
(2) calculating the ratio of expenditures for commercial fertilizers by county to expenditures for commercial fertilizers by State from the 1987 Census of Agriculture (U.S. Department of Commerce, 1989a); and
(3) computing annual county-level fertilizer sales, in tons, by multiplying estimates of annual State sales by the ratio of county expenditures to State expenditures.
Nitrogen-fertilizer sales estimates by county were constructed from estimates reported by the U.S. Environmental Protection Agency (1990) for 1985-89 and by Jerald Fletcher (West Virginia University, written commun., 1992) for 1990-91. The estimates of nitrogen-fertilizer sales in tons of actual nutrient were entered directly into the GIS. Nitrogen-fertilizer sales estimates are provided for each year (1985-91); however, the 1987 Census of Agriculture data on fertilizer expenditures used to disaggregate State sales totals represent only 1987 sales. Fertilizer-sales data submitted annually to State regulatory agencies by fertilizer dealers were compiled by the National Fertilizer and Environmental Research Center, TVA (U.S. Environmental Protection Agency, 1990). These data reflect total sales of fertilizer without regard to the land use for which it was bought, or the State (or county) in which the fertilizer was actually used.

Estimates of fertilizer sales by county were constructed from a combination of data reported to State regulatory agencies and from data in the 1987 Census of Agriculture. In the Census of Agriculture, sampling and statistics are used to account for nonresponding farm operations (U.S. Department of Commerce, 1989b). Thus, the information that describes county-level fertilizer sales is subject to sampling variability as well as reporting and coverage errors. Census disclosure rules also prevent the publication of information that would reveal the operation of individual farms.

Eleven attributes were added to an ARC/INFO coverage for each year of fertilizer-sales data. All attribute names contain a number that represents the year of the data. For example, NTOT86 is the attribute name for total nitrogen-fertilizer sales in 1986. Sales estimates are provided for total nitrogen, potash, and phosphate, and for nitrogen sold as ammonium nitrate, anhydrous ammonia, miscellaneous forms, nitrogen solutions, and urea. Nitrogen-fertilizer sales coverage names, attribute names, and short attribute descriptions are listed in table 3.

Fertilizer-use estimates for counties represented by one polygon are equal to county totals. For counties described by more than one polygon, fertilizer-use estimates are provided for each polygon and are calculated as the county total multiplied by the ratio of the area of the county polygon divided by the total area of the county. A missing-value code of -99.0 is used when no fertilizer-use estimate is available for a county and in all nonland-area polygons. A missing-value code in a county land polygon can indicate any of the following conditions:

-- fertilizer not sold in the county,
-- crop data withheld because of census disclosure rules,
-- crop data not available to the census, or
-- crop data not published because county contains fewer than 10 farms.

Census of Agriculture Data

Six coverages summarizing agricultural expenses, land use, chemical use, livestock holdings, and cropping practices were constructed from estimates reported by the U. S. Department of Commerce (1989a, 1989b) in the 1987 Census of Agriculture. A total of 123 data fields from the Census of Agriculture are summarized by 156 attributes in the 6 coverages. Most of the attributes summarized represent 1987 data, but some information from the 1982 Census of Agriculture also was included.

The estimates were constructed from surveys of all farms where $1,000 or more of agricultural products were sold, or normally would have been sold, during the census year. Sampling and statistics were used to account for nonresponding farm operations. Thus, the information in the Census of Agriculture is subject to sampling variability as well as reporting and coverage errors. Census disclosure rules prevent publication of information that would disclose the operation of individual farms. Thus, for example, one or two sod farms may be reported in a county, but no acreage of sod grown is reported, because release of that information might disclose information about a particular farmer's operation.

All census attributes were extracted from tabular data files provided by the U. S. Department of Commerce (1989a). Data are reported in either thousands of dollars, number, tons, acres, or percent of county. Attribute names are keyed to field names found in the technical documentation of the Census of Agriculture (U.S. Department of Commerce, 1989b). Specifically, the four-digit number at the end of the ARC/INFO item names matches the field-name numbers in the technical-documentation reference. Complete definitions of attributes and terms used in the census can be found in U. S. Department of Commerce (1989b; 1990). Census of Agriculture coverages and attribute names and short descriptions are listed in table 4. Attribute names beginning with CA represent data fields transferred directly from the census tabular data files. Attribute names beginning with PCT are percent-of-county attributes and represent relative intensities of an agricultural practice. Attributes reported as percent of county were calculated as the attribute value (in acres) divided by the county polygon area (in acres) multiplied by 100.

Census estimates for counties represented by one polygon are equal to county totals. For counties described by more than one polygon, attribute values are provided for each polygon and are calculated as the county total multiplied by the ratio of the area of each county polygon divided by the total area of the county. A missing-value code of -99 is used when no census-attribute data are given for a county and for all nonland-area polygons. A missing-value code in a county land polygon could indicate any of the following conditions:

-- agricultural practice not present in county (for example, no corn grown in county),
-- data withheld because of census disclosure rules,
-- data not available to census, or
-- data not published because county contains fewer than 10 farms.

OBTAINING AND USING THE GEOGRAPHIC INFORMATION SYSTEM COVERAGES

Obtaining the Coverages

The GIS coverages described in this report were prepared in compliance with the guidelines presented by Nebert (1994) for National-scope thematic data layers. These coverages are available through the U.S. Geological Survey Distributed Spatial Data Library (DSDL) (Nebert, 1994). DSDL is a distributed repository, and custody of specific data sets is assigned to individuals or groups within the organization. Complete documentation (metadata) and review of spatial and attribute information are required for all data sets prior to their inclusion in DSDL. Information in DSDL is accessible to the wide-area network and can be retrieved by using information-discovery programs such as the Wide Area Information Server (WAIS), gopher, or mosaic. The GIS coverages described in this report currently (1994) also can be made available on 1/4-inch tape or in DLG-O format upon special request to the Regional Hydrologist.

The coverages are retrievable as individual themes. The compressed ARC/INFO coverage export files range in size from 4.1 to 4.9 megabytes (MB). Uncompressed, these files range in size from 8.5 to 10.9 MB. All 18 uncompressed ARC/INFO coverage export files occupy about 170 MB of disk space. All 18 imported ARC/INFO coverages occupy about 100 MB of disk space. Generally, about 200 to 300 MB of disk space is required to work with data sets of this size. Instructions for on-line data retrieval are given in appendix 1.

Use of the Coverages

The information on agricultural-chemical use, land use, and cropping practices presented in this report are intended for use directly in a geographic information system. Several aspects of the processing of this information into GIS coverage format are important when working with the data. First, census disclosure rules affect the content of all of the coverages. In some cases the absence of a reported value for a particular attribute in a particular county is the result of census disclosure rules rather than a true zero value for the attribute in that county. Second, for counties described by more than one polygon, attribute values are provided for each polygon and are calculated as the county total multiplied by the ratio of the area of each county polygon to the total area of the county. This operation makes the coverage easier to work with in the GIS but also means that care must be used when the information in the coverages is used to estimate total attribute values for counties described by more than one polygon. Most of the counties in the coverages are represented by only one polygon, however. Third, additional details on coverage preparation, item definitions, and coverage projection are given in the on-line coverage documentation files (see example in appendix 1). Not all of the documentation files were printed in this report because of their length (about 35 pages each). The GIS coverage attributes that are accessible to users are listed in tables 1-4.

The information summarized in the coverages provided is intended for use in estimating regional agricultural-chemical use, land use, or cropping practices, and in producing visual displays and mapping relative rates of agricultural-chemical use, land use, or cropping practices across broad regions of the United States (Battaglin and Goolsby, 1994; Battaglin and others, 1993; Goolsby and others, 1993; Goolsby and Battaglin, 1993; Mueller and others, 1993). The estimates provided can not be used appropriately to determine rates of agricultural-chemical use or the presence or absence of a particular agricultural practice in small areas (less than 20 square miles) or at specific locations.

SUMMARY

Eighteen geographic information system spatial data layers (coverages) summarizing for all counties in the conterminous United States the use of 96 herbicides in 1989; the annual sales of nitrogen fertilizer, for 1985-91; and agricultural expenses, land use, chemical use, livestock holdings, and cropping practices in 1987 are discussed in this report and are available through the U.S. Geological Survey Distributed Spatial Data Library (DSDL). Information in DSDL is accessible to the wide-area network. The information in these coverages is intended for use in estimating regional agricultural-chemical use, land use, or cropping practices, and in producing visual displays and mapping relative rates of agricultural-chemical use, land use, or cropping practices across broad regions of the United States.

The 18 coverages were constructed by relating tabular source materials to a polygon coverage representing county boundaries, lakes, estuaries, and other nonland-area features in the conterminous United States at a scale of 1:2,000,000.

SELECTED REFERENCES

Aho, Alfred V., Kernighan, Brian W., and Weinberger, Peter J., 1988, The AWK programming
language: New York, Addison-Wesley Publishing Company, 210 p.
Alexander, Richard B., and Smith, Richard A., 1990, County-level estimates of nitrogen and
phosphorus fertilizer use in the United States, 1945 to 1985: U.S. Geological Survey Open-File Report 90-130, 12 p.
Battaglin, W.A., Goolsby, D.A., and Mueller, D.K., 1994, Relations between use, concentration,
and transport of agricultural chemicals in the Mississippi River basin, in Marston, R.A., and Hasfurther, V.R., eds., Effects of human-induced changes on hydgrologic systems, proceedings of the American Water Resources Association Summer Symposium, Jackson Hole, Wyoming, June 26-29, 1994, p. 1073-1086.
Battaglin, W.A., Goolsby, D.A., and Coupe, R.H., 1993, Annual use and transport of agricultural
chemicals in the Mississippi River, 1991-92, in Goolsby, D.A., and others, eds., Selected papers on agricultural chemicals in water resources of the Midcontinental United States: U.S. Geological Survey Open-File Report 93-418, p. 26-40.
Battaglin, W.A., and Goolsby, D.A., 1994, Relations between herbicide use and annual transport of
herbicides in Midwestern rivers, 1991-92, in Weigmann, D. L., ed., New directions in pesticide research, development, management, and policy, Proceedings of the Fourth National Conference on Pesticides, November 1-3, 1993, p. 711-723.
Burkart, M.R., and Kolpin, D.W., 1993, Hydrologic and land-use factors associated with
herbicides and nitrate in near-surface aquifers: Journal of Environmental Quality, v. 22, no. 4, p. 646-656.
Domeratz, M.A., Hallam, C.A., Schmidt, W.E., and Calkins, H.W., 1983, USGS digital cartographic
data standards--Digital line graphics from 1:2,000,000-scale maps: U.S. Geological Survey Circular 895-D, 38 p.
Environmental Systems Research Institute, 1992, AML user's guide: Redlands, Calif.,
Environmental Systems Research Institute, Inc., various pagination.
Gianessi, Leonard P., and Puffer, Cynthia, 1991, Herbicide use in the United States:
Washington, D.C., Resources for the Future, December 1990 (revised April 1991), 128 p.
Goolsby, D.A., and Battaglin, W.A., 1993, Occurrence, distribution and transport of agricultural
chemicals in surface waters of the midwestern United States, in Goolsby, D.A., and others, eds., Selected papers on agricultural chemicals in water resources of the Midcontinental United States: U.S. Geological Survey Open-File Report 93-418, p. 1-25.
Goolsby, D.A., Battaglin, W.A., and Thurman, E.M., 1993, Occurrence and transport of
agricultural chemicals in the Mississippi River Basin, July through August 1993: U.S. Geological Survey Circular 1120-C, 22 p.
Goolsby, D. A., Coupe, R.H., and Markovchick, D. J., 1991b, Distribution of selected herbicides and
nitrate in the Mississippi River and its major tributaries, April through June 1991: U.S. Geological Survey Water-Resources Investigations Report 91-4163, 35 p.
Goolsby, D.A., Thurman, E.M., and Kolpin, D.W., 1991a, Herbicides in streams--Midwestern
United States, in Irrigation and drainage, Proceedings of the 1991 American Society of Civil Engineers Conference, Honolulu, Hawaii, July 22-26, 1991, p. 17-23.
He, Chansheng, Riggs, James F., and Kang, Yung-Tsung, 1993, Integration of geographic
information systems and a computer model to evaluate impacts of agricultural runoff on water quality, in Harlin, J.M., and Lanfear, K.J., eds., Proceedings of the Symposium on Geographic Information Systems and Water Resources: American Water Resources Association Technical Publication Series TPS-93-1, Mobile, Ala., March 14-17, 1993, p. 61-70.
Kolpin, D.W., Goolsby, D.A., Aga, D.S., Iverson, J.L., and Thurman, E.M., 1993, Pesticides in
near-surface aquifers--Results of the Midcontinental United States ground-water reconnaissance, 1991-92, in Goolsby, D.A., and others, eds., Selected papers on agricultural chemicals in water resources of the Midcontinental United States: U.S. Geological Survey Open-File Report 93-418, p. 64-74.
Madison, R.J., and Brunett, J.O., 1985, Overview of the occurrence of nitrate in ground water of
the United States, in National Water Summary 1984--Hydrologic events, selected water-quality trends, and ground-water resources: U.S. Geological Survey Water-Supply Paper 2275, p. 93-105.
Mueller, D.K., Ruddy, B.C., and Battaglin, W.A., 1993, Relation of nitrate concentrations in
surface water to land use in the upper-midwestern United States, 1989-90, in Goolsby, D.A., and others, eds., Selected papers on agricultural chemicals in water resources of the Midcontinental United States: U.S. Geological Survey Open-File Report 93-418, p. 41-50.
Nebert, Douglas D., 1994, Design of the distributed spatial data library for the Water Resources
Division, U.S. Geological Survey: U.S. Geological Survey Open-File Report 94-327, 30 p.
Rains, L., and Latham, P., 1993, GIS modelling of land use and associated nonpoint source
pollution, in Harlin, J.M., and Lanfear, K.J., eds., Proceedings of the Symposium on Geographic Information Systems and Water Resources: American Water Resources Association Technical Publication Series TPS-93-1, Mobile, Ala., March 14-17, 1993, p. 35-44.
Rinehold, J.W., and Witt, J.M., 1989, Oregon pesticide use estimates for 1987: Corvallis Oregon
State University Extension Service, various pagination.
Scribner, E.A., Thurman, E.M., Goolsby, D.A., Meyer, M.T., Mills, M.S., and Pomes, M.L., 1993,
Reconnaissance data for selected herbicides, two atrazine metabolites, and nitrate in surface water of the midwestern United States, 1989-90: U.S. Geological Survey Open-File Report 93-457, 77 p.
Spalding, R.F., and Exner, M.E., 1991, Nitrate contamination in the contiguous United States, in
Bogardi, I., and Kuzelka, R.D., eds., Nitrate contamination--Exposure, consequence, and control: Berlin, Springer-Verlag, North Atlantic Treaty Organization Advanced Science Institutes Series, v. G 30, p. 13-48.
Thurman, E.M., Goolsby, D.A., Meyer, M.T., and Kolpin, D.W., 1991, Herbicides in surface water
of the midwestern United States--The effect of the spring flush: Journal of Environmental Science and Technology, v. 25, no. 10, p. 1794-96.
Thurman, E.M., Goolsby, D.A., Meyer, M.T., Mills, M.S., Pomes, M.L., and Kolpin, D.W., 1992, A
reconnaissance study of herbicides and their metabolites in surface water of the midwestern United States using immunoassay and gas chromatography/mass spectrometry: Journal of Environmental Science and Technology, v. 26, no. 12, p. 2440-2447.
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U.S. Department of Agriculture, Economic Research Service, February, Washington, D.C.
U.S. Department of Agriculture, 1989b, Agricultural resources--Situation and outlook report:
U.S. Department of Agriculture, Economic Research Service, August, Washington, D.C.
U.S. Department of Commerce, 1989a, Census of agriculture, 1987--Final county file: U.S.
Department of Commerce, Bureau of the Census [machine-readable data file].
________ 1989b, Census of agriculture, 1987-- Final county file technical documentation:
U.S. Department of Commerce, Bureau of the Census, Data User Services Division, various pagination.
________ 1990, Census of agriculture, 1987-- Agricultural atlas of the United States,
volume 2: U.S. Department of Commerce, Bureau of the Census, Agriculture Division, AC87-S-1, 210 p.
U.S. Environmental Protection Agency, 1990, County-level fertilizer sales data: U.S.
Environmental Protection Agency, Office of Policy, Planning, and Evaluation, PM-221.
________ 1992, Another look--National pesticide survey phase II report,
Washington, D.C., 174 p.
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Washington, D.C., U.S. Geological Survey, 417 p.

APPENDIX 1. Data Specifications and Retrieval Documentation

Choose any file to see the documentation, or "metadata." The metadata contains instructions for on-line retrieval.

Storage Requirements

The 18 files represent about 80 megabytes (MB) of raw binary data. The compressed ARC/INFO coverage export files range in size from 4.1 to 4.9 MB. Uncompressed, these files range in size from 8.5 to 10.9 MB. The 18 uncompressed ARC/INFO coverage export files will occupy about 170 MB of disk space. The 18 imported ARC/INFO coverages will occupy about 100 MB of disk space. In general, about 200 to 300 MB of disk space will be required to work with data sets of this magnitude.

Recommended Directory Structure

All of the coverages can be stored under one directory, or separate directories can be made for the Census of Agriculture, herbicide-use, nitrogen-fertilizer sales, and other National extent and scale coverages. To prevent corruption or unwanted modification of the coverages provided, create a large work space for manipulation and processing involving the coverages. Copy coverages to the work space before executing any ARC, ARCEDIT, ARCPLOT, or GRID commands that may affect coverage topology or attributes. Failure to make working copies of the coverages could result in the corruption of the original data or in the loss of the metadata describing coverage construction and attributes.

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Revision 0: 1020 23JAN96 Lorna Schmid Kendrix
Revision 1: 1246 22JAN97 kjl Added references to Alexander and Smith.