Tracking urban sprawl: Using spatial data to inform farmland preservation policy

The development of state farmland preservation policies has primarily relied upon results of the Census of Agriculture that is updated every 5 years by the USDA National Agriculture Statistics Service. Questions about the suitability of the Census of Agriculture center on the measures of total farmland and total cropland as reported by agricultural producers. The reliance on these variables fails to distinguish between conversion to developed uses and other fluctuations in the total availability of farmland. This inability to directly measure farmland conversion to developed uses has been shown to influence state level farmland preservation policies. The policies of Illinois and Indiana highlight the disparate approaches, with Illinois pursuing an intensive policy to protect farmland and Indiana choosing to not address farmland preservation at a state level. In order to assess the suitability of the different approaches to farmland preservation policy it is critical to evaluate the Census of Agriculture data used to justify the policies of Illinois and Indiana.This study focuses on using spatial analysis to determine the rate of farmland conversion to developed uses in all counties in Indiana and Illinois. The spatial analysis utilizes the 1992 USGS National Land Cover Dataset and the 2002 NASS Cropland Data Layer along with other supporting data layers to compare with results from the 1992 and 2002 Census of Agriculture datasets. The spatial analysis supports the trends identified in the National Resources Inventory that show farmland conversion is occurring at a higher rate than is reported by the Census of Agriculture. As a result, implications for state level policies in Illinois and Indiana are discussed as well as the potential for utilizing spatial data to inform farmland preservation policy throughout the United States.