Developing Criteria for Delineating Urban Areas
Michael Ratcliffe of the U.S. Census Bureau stressed that his presentation would not describe proposed criteria, but rather ideas to generate feedback for use in preparing proposed criteria for the definition of urban areas. He noted that the U.S. Census Bureau has officially defined urban areas since 1910, that they define urban areas after each census, and that the areas are defined for statistical—not programmatic—purposes. The criteria are reviewed and revised before each census, but a common theme over the decades has been to identify the built-up, densely settled urban landscape. The population threshold of 2,500 is an enduring part of the changing definitions.
Adopted in 1950, the density-based urbanized area (UA) concept allowed for the inclusion of more than just incorporated areas, and even noncontiguous areas. The UA concept was largely unchanged over the following decades, and the delineation of areas required a labor-intensive, interactive paper map–based process that involved some amount of subjectivity (e.g., in deciding whether a nearby densely settled area was part of a UA). The inclusion of nearby areas often requires the use of “jumps” or “hops” over unsettled or less-dense areas. Although whimsical sounding, these are technical terms, with jumps generally limited to a single jump (in a given direction) of no more than 1.5 miles, but hops permitting multiple spans of up to 2.5 miles.
For 1990, the U.S. Census Bureau published UA criteria in a Federal Register notice for the first time and used interactive delineation software. The process was more automated, but still required subjectivity—as in the application of hops, which were first used in 1990. For 2000, the UA concept was supplemented with urban clusters (UCs)—the same concept, but applied to smaller areas. UAs have populations of 50,000 or more, and UCs have populations of 2,500–50,000.
Ratcliffe described how the use of automated software has shifted the focus from which areas to include in UAs to questions of where to split large urban areas. If fully automated, the process would possibly split urban areas in the middle of a downtown business district or identify a single continuous UA from Wilmington, Delaware, to Springfield, Massachusetts—and, by rule, call it New York.
Issues for 2010 include identifying nonresidential urban land uses on the fringe of UAs, establishing objective methods for splitting large urban agglomerations, comprehensively identifying undevelopable territory (e.g., wetlands and steep slopes), and delineating UAs in Puerto Rico and the island areas. Looking beyond 2010, a challenge will be how to incorporate annual data from the ACS and the possible definition of “suburban” and “exurban” areas.
Chris Henrie of the U.S. Census Bureau reinforced two major points: the continued use of the 2,500 population threshold and the fact that the threshold no longer relates to incorporated areas. Henrie then filled in with helpful details about the application of jumps and hops, the exemption of areas such as parks, and other issues in the inclusion/exclusion of discontiguous areas. He also described options being explored, including the greater use of census tracts (allowing for greater use of commuting data) and the use of data on impervious (paved) land surfaces and steep slopes. The bureau is also reconsidering the importance of the concept of the central place to the realistic delineation of urban areas. Above all, Henrie stressed that the U.S. Census Bureau remains committed to an objective, equitable, and consistent nationwide delineation of urban areas.
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