Appendix A. Details (including resolution, datum, and accuracy) for candidate predictor variables used in the modeling process.
For the variable BROAD_92, other rural land included such features as farmstead and ranch headquarters, windbreaks, feedlots, nurseries, greenhouses, and barren land.
For the variable L_CAP_92, land capability class indicated the suitability of the soil for most kinds of field crops based on landscape location, slope, soil depth, texture, and reaction of the soil (Helms 1992:60). Not applicable referred to cases where the land was no longer available for crop production (e.g., converted to developed land).
The variable ELEV was derived from the National Elevation Dataset (Gesch et al. 2002, Gesch 2007), a raster data set with 1-arc-second (~30 m) horizontal resolution, 0.1 m vertical resolution, and an average absolute vertical accuracy of 2.4 m. The horizontal datum is the North American Datum of 1983 (NAD 83), and the vertical datum is the North American Datum of 1988 (NAVD 88).
All landscape variables except road density (RD_DEN) were derived from the National Land Cover Data (circa 1992 imagery, 30-m resolution) using a land type classification adapted from Anderson Level 1 classes (Anderson et al. 1976) as defined in Vogelmann et al. (2001). Classification accuracies for land types used in the present analysis for the Southeast Region of Stehman et al. (2003) were as follows: open water (97%); developed (72%); forest (91%); agriculture (83%); and wetland (82%). Road density was based on U.S. Bureau of Transportation Statistics with a nominal date of 1999 (http://rmgsc.cr.usgs.gov/trip/data/); date range was 1991–2001 (Supporting Online Material in Watts et al. 2007).
Anderson, J. F., E. E. Hardy, J. T. Roach, and R. E. Witmer. 1976. A land use and land cover classification system for use with remote sensor data. U.S. Geological Survey Professional Paper 964, Washington, D.C., USA.
Gesch, D. B. 2007. Chapter 4 – The National Elevation Dataset. Pages 99–118 in D. Maune, editor. The DEM user’s manual. Second edition. American Society for Photogrammetry and Remote Sensing, Bethesda, Maryland, USA.
Gesch, D., M. Oimoen, S. Greenlee, C. Nelson, M. Steuck, and D. Tyler. 2002. The National Elevation Dataset. Photogrammetric Engineering and Remote Sensing 68:5–11.
Helms, D. 1992. The development of the land capability classification. Pages 60–73 in Readings in the history of the Soil Conservation Service. Economics and Social Sciences Division, NHQ. U.S. Department of Agriculture, Soil Conservation Service, Washington, D.C., USA.
Stehman, S. V., J. D. Wickham, J. H. Smith, and L. Yang. 2003. Thematic accuracy of the 1992 National Land-cover Data for the eastern United States: statistical methodology and regional results. Remote Sensing of Environment 86:500–516.
Vogelmann, J. E., S. M. Howard, L. Yang, C. R. Larson, B. K. Wylie, and N. Van Driel. 2001. Completion of the 1990s National Land Cover Data Set for the conterminous United States from Landsat Thematic Mapper data and ancillary data sources. Photogrammetric Engineering and Remote Sensing 67:650–662.
Watts, R. D., R. W. Compton, J. H. McCammon, C. L. Rich, S. M. Wright, T. Owens, and D. S. Ouren. 2007. Roadless space of the conterminous United States. Science 316:736–738.