Appendix F

Generally speaking, an Urbanized Area must exhibit a pattern of continuous development outward from a central core. Although there are special provisions for "jumps," and certain other exceptions, by and large, new areas added every 10 years by the Census Bureau to the adjacent urban fringe must be contiguous to that fringe and must have a population density of at least 1,000 people per square mile.

Population density can be determined by dividing the population of census tracts and blocks by their land area. In actuality, the Bureau does not ascertain what percentage of a given tract or block is paved or built upon; it is simply assumed to be "urbanized" if it has a population density of 1,000 per square mile. The Bureau allows exceptions to the density criterion when other criteria for "jumps," non-residential urban land use, closure of indentations and enclaves, and undevelopable territory are met.

Delineating Urbanized Areas is a large, labor-intensive endeavor. In order to more efficiently and accurately delineate Urbanized Areas in the 1990 census, the Census Bureau automated much of the task by using the TIGER (Topologically Integrated Geographic Encoding and Referencing) database and customized UA delineation software. In the near future, we will issue another study that analyzes the Urbanized Areas data that have only recently become available from the 2000 Census.

Difference from MSA Designation. Urbanized Areas are smaller in area than the Metropolitan Statistical Areas (MSA) that are mentioned far more commonly in the media and other public discussion. The Census Bureau describes an MSA as "a large population nucleus, together with adjacent communities having a high degree of social and economic integration with that core."²⁰⁹  The major difference between the Urbanized Area and the MSA is that the latter includes the entire land mass of every county that contains a part of a city and its suburbs. That means the outer parts of an MSA are rural. An Urbanized Area, on the other hand, includes whole counties only if every square mile of them is urbanized. And in the outer counties, only the land that is indeed urbanized is counted.

An MSA often lumps together cities that have substantially grown out toward each other but which may still contain some rural land between them. For example, Los Angeles and its contiguous suburbs in Orange and Los Angeles counties, Simi Valley and its suburbs, Oxnard-Ventura and their suburbs, and San Bernardino and Riverside and their suburbs are all classified as a single CMSA (Consolidated Metropolitan Statistical Area). But because there is some rural land remaining between the suburbs of one and the suburbs of another, these places are considered to be four separate Urbanized Areas.

Usefulness as a Measuring Tool. The 1,000-people-per-square-mile threshold for classification as part of an Urbanized Area is not without its critics. For example, urban expert David Rusk believes that the growth in Urbanized Land Areas since 1950, as documented in successive Census Bureau reports, understates the actual loss of rural environments to sprawl.²¹⁰  The 1,000 density threshold (equal to about one dwelling per two acres) is arguably too dense to convey a rural "feel" and allow for unfettered rural livelihoods, like farming. On the other hand, there is still a substantial amount of open space left when there is an average of two acres (about two football fields) for each house. Nonetheless, the practice of designating a given site as either urban or rural, with no intermediate classification, is indeed an over-simplification.

Yet for the purposes of this study, shortcomings of the Census designations have little effect on the outcome. Since this study has defined sprawl as the progressive loss of open space to built-up space — unpaved lands to paved-over ground in other words — the 1,000-per-square-mile criterion is as defensible a threshold between urban and rural zones as any. Moreover, it allows use of the Census Bureau’s nationwide, unrivalled stock of information. The strength of the Census Bureau’s uniform data set lies in calculating changes from rural to urban areas rather than in precisely defining the line that divides them. The shortcoming of the Census Bureau measurement is in calculating total development, not in calculating change. This study focuses on the change.

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Endnotes

²⁰⁹ www.census.gov/population/www/estimates/metroareas.html

²¹⁰ David Rusk. 1999. Letter to Ms. Georgia Masters, Department of Community Economic Development, State of Pennsylvania, Harrisburg. July 12. Rusk is an independent consultant on urban and suburban policy, the author of Cities without Suburbs, and the former mayor of Albuquerque, New Mexico.