James T. Carrington
USDA, Natural Resources Conservation Service
National Cartography and Geospatial Center
501 Felix Street
Fort Worth, Texas 76115
USA
This paper describes the use of ArcView software by the United States Department of Agriculture, Natural Resources Conservation Service (NRCS) to integrate 1997 National Resources Inventory data. The National Resources Inventory is a collection of natural resources information of non-Federal land in the Unites States. These data provide information that is used to formulate effective agricultural and environmental policies and legislation, implement resource conservation programs, and provide a picture of many our nation's natural resources and conditions. This paper illustrates how NRI data can be brought into ArcView - the NRCS GIS package - and cartographic products and reports can be generated easily.
The Natural Resources Conservation Service (NRCS) recently released National Resources Inventory (NRI) data to the public. The current version, 1997 National Resources Inventory (Revised December 2000), CD-ROM - Version 1 (December 2001) is available through online ordering at http://www.ftw.nrcs.usda.gov/nri_order.html. The NRI is a scientifically designed, longitudinal panel survey of the Nation's soil, water, and related resources designed to assess conditions and trends every 5 years. The NRI is conducted by the NRCS in cooperation with the Iowa State University (ISU) Statistical Laboratory. The 1997 NRI contains data from non-Federal and water areas within the 48 conterminous United States, Hawaii, Puerto Rico, and the U.S. Virgin Islands. The 1997 NRI provides results that are consistent for all non-Federal lands for four points in time - 1982, 1987, 1992, and 1997. The historical 1982, 1987, and 1992 data were updated to reflect 1997 technical criteria and protocols as part of the 1997 NRI inventory process. The 1997 NRI database should be considered self-contained in that respect.
The NRI database is a statistical database. The data do not come in a summarized or aggregated form. Users of the database decide which portions of the data are needed and how to aggregate and summarize the data most effectively. The data must be aggregated to develop meaningful statistics and analyses. To use the individual sample point data as other than a part of the statistical database is inappropriate.
Tabulations made from the NRI database are estimates - not absolute facts. These tabulations produce estimates rather than facts because they are based upon sample data derived from a survey rather than data coming from a census or complete measurement. Each estimate has some degree of statistical uncertainty associated with it; this statistical uncertainty affects analyses of the data and interpretation of results.
NRI data were collected at more than 800,000 sample sites nationwide. This is a large sample, which means that the data can be legitimately used to analyze issues at many geographic levels -- national, regional, state, and sub-state (multi-county). However, the NRI was not designed for analyzing issues at the county level.
The precision of NRI estimates depends upon the number of samples within the region of interest, the distribution of the resource characteristics across the region, and the sampling procedure. Characteristics that are common and spread fairly uniformly over an area can be estimated more precisely than characteristics that are rare or unevenly distributed.
Measures of uncertainty (margins of error, standard errors, or confidence intervals) should be taken into consideration in all data analyses. Data users who have limited experience in using sample survey data are advised to seek professional assistance regarding the statistical implications of the data. It is advisable to work in teams when utilizing the NRI for a scientific project. This analysis team should include someone who has statistical analysis skills, can explain and interpret statistical uncertainty and sampling error, and can offer guidance for the generation and interpretation of the NRI estimates.
The NRI design objectives should not be thought of as a restriction to full analytical use of the NRI database. Examining data at various geographic levels is a legitimate analytical technique -- it is a particularly valuable way to gain additional insights into the database and in discovering "messages" that can be pulled from the data. Users of the 1997 NRI database can initially analyze the data at a fairly localized level, paying close attention to the margins of error of the estimates at those localized levels. Data can then be aggregated to higher levels for display or presentation purposes. Estimates at these aggregated levels would have sufficiently narrow confidence intervals so that results would be appropriate for presentation and discussion. More technical information about the 1997 NRI is available at: http://www.nrcs.usda.gov/technical/NRI.
In the past NRCS data users have used an online system to make use of the 1997 NRI data. This system, called OASYS, is an Internet-based query builder that uses e-mail to send a text report back to the requestor. It is available to NRCS staff only, so requests from the public have necessitated a trained NRCS resource person to run the query. NRCS has used ArcView software for some time. Recently, the Common Computing Environment (CCE) was implemented for the three Service Center Agencies - NRCS, Farm Services, and Rural Development. This CCE enables the use of a Customer Service Toolkit to the new, more powerful computers located in the field office. The Toolkit is a collection of software tools, including some ArcView Extensions, for USDA field employees who work with the public, primarily with farmers and ranchers. It will also be useful to partner agencies, such as Conservation Districts and State Departments of Natural Resources, or others who provide conservation planning and resource assessment information.
The purpose of the tools is to help natural resource planners provide information to the public that results in conservation on the land. Software tools incorporate commercial software products that enable conservationists to provide natural resource information in professional looking products.
The Toolkit also provides tools for mapping and analyzing natural resource information. Maps are a traditional method of communicating with customers, and the Toolkit makes it easy to develop these maps for customers. With the use of Microsoft Access or other database management software packages, the NRI data can be brought into ArcView and cartographic products produced quickly.
The steps to producing a national map are as follows:
With the steps shown above, the 1997 NRI Data can be easily manipulated and moved into ArcView software. Depending on the user's skills in Access, many types of queries can be created and run to perform analyses of the data. Once queries have been run, creation of various cartographic products is up to the user's skill and discretion in ArcView. It is my hope that a NRCS field employee desiring to utilize the 1997 NRI Data will make use of these similar steps to map out data in ArcView.
James T. Carrington
USDA, Natural Resources Conservation Service
National Cartography and Geospatial Center
501 Felix Street
Fort Worth, Texas 76115
USA
Phone: 817-509-3357
Fax: 817-509-3486
E-mail: jcarring@ftw.nrcs.usda.gov