RUCAs are one of many ways to measure the concept of rural and not the only approach. It is important that end users understand what the various methods are and to use them only when they are appropriate.
The RUCA codes (Version 2) consist of 33 codes. These codes can be combined in many different ways depending on the purpose of the user. This is why the taxonomy was created with the 33 separate codes. While the creators of the taxonomy suggest some ways to aggregate the codes, these are generic suggestions, and each user should review what the best aggregation is for the purpose at hand. Different federal and state entities (e.g., CMS, ORHP, CDC, and WA DOH) and researchers have aggregated the codes different ways to meet their needs. Usually these aggregations are dichotomous (i.e., rural versus urban). The creators of the taxonomy do not take responsibility for the choices of others concerning the aggregation of the codes. On some occasions, those influenced by the third party aggregations to determine their eligibility for programs or research results are critical of the RUCA taxonomy when the problem is actually how the codes were aggregated. The RUCA codes can be custom aggregated to fill a plethora of purposes. They can also be combined with other data to refine the way they target certain types of areas (ZIP code poverty information – all 10s with 20% of their population below poverty level). They can be used in combination with the Remote Tools provided in this web page (e.g., all 10.0 codes more than 60 minutes travel from an Urbanized Area (RUCA code 1s). The RUCAs may be inappropriate for certain policy or research needs.
RUCA ZIP versions are not designed to be compared across time. Version 1.11 and Version 2.0 are based on work commuting patterns from different times (1990 and 2000) and different ZIP code years (1998 and 2004). The underlying Census tracts changed quite dramatically between 1990 and 2000. The Census Bureau added hundreds of Urbanized Areas and Urban Clusters between 1990 and 2000, and even changed the definitions of how these entities are determined. The RUCA coding scheme and criteria were changed slightly from Version 1.11 to Version 2.0. For these reasons, showing trends across time using different versions of RUCAs is not appropriate.
The ZIP code version of the Census tract-based RUCAs is an approximation (albeit a close one). Information on this web site shows some vital statistics from the perspective of matching the Census tracts. However, it should be kept in mind that the Census tracts are not an ideal unit in the first place (although often, but not always, geographically smaller). An argument can also be made about the suitability of use of ZIP code areas.
Work commuting in the smallest ZIP codes can be based on a small number of Census responses (note that a variable is provided in the file about the relative population of the ZIPs).
The RUCA codes are not a continuum from urban to rural with numbers starting at 1.0 and ending at 10.6 and should not be used as such. Each code has a specific meaning. For instance, code 10.1 in most contexts is clearly more urban related than code 9.0.
The estimated road travel times and distances are actual estimates (i.e., not exact). The times and distances are measured along the estimated fastest road route to the closest type of geographic unit (e.g., Urbanized Area or Large Urban Cluster). The trips are calculated from the nearest road to the ZIP codes’ population centroid.
Estimates of the size of the Census Urbanized Area and Urban Cluster associated with the primary and secondary work commuting flows and the type of Census unit the ZIP code/Census tract is part of are approximations. The approximation from Census tracts to ZIP codes causes some small generalizations and only the two largest commuting flows were considered in the assignment algorithm.
The assigned Census tract and ZIP code RUCAs for Puerto Rico are approximations. The Census Bureau had problems with the commuting data for Puerto Rico, so we made the assignments without these data. Thus, the RUCAs for Puerto Rico only take on the values of 1, 4, 7, and 10.
While the Census tract and ZIP code RUCAs are a vast improvement in rural/urban definitions based on counties (significant issues of over- and under-bounding the actual Urbanized Areas and Urban Clusters), there are still some Census tracts and ZIP Code areas that are geographically very large. Thus, some towns may receive codes that seem inappropriate because they are included with larger or smaller places.