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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.
Contrasts with Measures of Urban Influence
Given the importance and ubiquity of the land conversion issue,
it is not surprising that numerous sets of statistics have been
developed that attempt to measure the extent of conversion and its
effects on agriculture. For some time, ERS has provided the research
community with county-level classifications (codes) that delineate
rurality and urban influence, classifying counties into ordinal
categories according to the amount of urban influence to which
the counties are subject (e.g., ERS county-level urban
influence codes and rural-urban
continuum codes). These classification schemes are implemented
using alternative methods to categorize counties according to size
of metropolitan core-county population, physical adjacency to metropolitan
core counties, and commuting patterns (e.g., see Measuring
Rurality Briefing Room. An advantage of county-level measures
of urban influence is that they are compatible with the many U.S.
statistical data series that provide data at the county level. More
recently, ERS has developed rural-urban
commuting area codes (RUCAs), which are based on sub-county
units called census tracts. The RUCAs are especially useful in applications
where geographic units smaller than counties are of interest. RUCAs
have been widely adopted for use in health-care studies and programs.
For an increasing number of applications, however, classifications
for even smaller spatial areas and spatial points (specific latitudes
and longitudes) would be useful. The increasing availability of
geo-located data, and Geographic Information Systems (GIS) software
for its analysis, motivates an additional system. Ideally, that
system is complementary to the county-level and census-tract schemes
cited above, but capable of classifying even smaller sub-county
spatial areas according to the amount of urban-related population
interaction to which they are subject. The PIZA codes are a newly
available measure that attempts to satisfy that need while providing
a bridge to county level measures. In addition, the PIZA codes provide
a continuous measure of population interaction, which is more useful
for some applications than are the existing ordinal measures.
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