Note: Updates to this data product are discontinued.

Widespread conversion of rural lands to urban uses has drawn attention at all levels of government. To provide information useful for projections of future changes in land use, ERS has created a system to classify remaining farmland into "population-interaction zones for agriculture" (PIZA). These zones represent areas of agricultural land use in which urban-related activities (residential, commercial, and industrial) affect the economic and social environment of agriculture. In these zones, interactions between urban-related population and farm production activities tend to increase the value of farmland, change the production practices and enterprises of farm operators, and elevate the probability that farmland will be converted to urban-related uses.

The PIZA codes are derived from a classification scheme that indexes small geographic areas according to the size and proximity of population concentrations. Designation of the zones begins with use of common GIS software to assign an index number to each of many small (five-kilometer) grid cells laid out (figuratively) across the contiguous 48 States. These "population-interaction indexes" (PII) are designed to provide a cardinal measure of the potential interaction between nearby urban-related population and agricultural production activities in each grid cell. (By a cardinal measure, we mean that the codes effectively rank each location or area on a continuous scale.) The population-interaction indexes are based on the regional economist's or geographer's concept of a "gravity" model, which provides measures of accessibility to population concentrations. This model measures population interaction by accounting for the size of all populations in the proximity of a given location or grid cell and the distance of that location or grid cell from those populations.