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A Comparison of GIRAS Agricultural Land- Use Data with 1994 Large-Scale Agricultural Land-Use Data

U.S. Geological Survey National Computer Technology Meeting
By Douglas J. Newcomb

Abstract

A major component of the Albemarle-Pamlico drainage study unit of the U.S. Geological Survey's National Water-Quality Assessment Program (ALBE-NAWQA) is the investigation of possible correlations between land use and water-quality characteristics in various subbasins. Subbasin boundaries, digitized from 1:24,000-scale maps, were used to characterize land use in small (less than 60 square miles in area) basins from U.S. Geological Survey 1:250,000-scale GIRAS (Geographic Information Retrieval and Analysis System for Handling Land Use and Land Cover Data) land-use data, digital maps based on photointerpretations completed in the mid-1970's. The agricultural areas from the basin-clipped GIRAS data were totaled and compared to 1994 crop and animal data provided by the U.S. Department of Agriculture`s Consolidated Farm Service Agency (CFSA) and Natural Resource Conservation Service (NRCS).

The purpose of the analysis was to determine if there were significant differences in agricultural land use estimated by using the two methods. Differences in basin area between the cropland-pasture GIRAS classification and the CFSA cultivated-crop data for 1994 ranged from 1 to 48 percent of basin area. Of the 21 basins studied, GIRAS Confined Feeding Operations data consistently underestimated the presence of these operations when compared to the 1994 NRCS data.

Newcomb, D.J., 1996, A comparison of GIRAS agricultural land-use data, with 1994 large-scale agricultural data: U.S. Geological Survey National Computer Technology Meeting, May 20.