Rural Urban Commuting Areas (RUCA) are assigned to ZIP Codes using population and commuting information from the Census. They form a classification scheme that distinguishes urban ZIP Codes by population size and characterizes rural ZIP Codes by their population and the strength of their association with larger urban areas. Rural ZIP Codes are differentiated by three factors; the size of their largest urban community, the proportion of that population regularly commuting to larger urban areas, and the size of the urban destinations. RUCA are defined for 1993 ZIP Codes using population and commuting information from the 1990 census.
PL_RUCA4 is created using a method recommended by RUCA's developers for combining the 30 categories defined by the full RUCA into a few broader categories suitable for health care analysis. The full RUCA is collapsed into PL_RUCA4 using this translation:
||1.0, 1.1, 2.0-2.2, 3.0, 4.1, 5.1, 7.1, 8.1, 10.1
||Large rural town
||4.0, 5.0, 6.0
||Small rural town
||7.0, 7.2-7.4, 8.0, 8.2-8.4, 9.0-9.2
This approach produces four classes by combining categories defined by the population and primary destination of commuting flows of a ZIP Code. This definition is especially sensitive to commuting as a measure of urban influence. If large secondary commuting flows (> 30%) connect it with a more heavily urbanized area, a more urbanized category is assigned than the ZIP Code's population alone would dictate.