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 national and State levels (for some individual counties and UAs the effects have been more evident).

Since the 1970 census, changes in the minimum size criterion to qualify as a central place have permitted the delineation of UAs around smaller population centers. For 1990, there was no size requirement for a central place. The inclusion of CDPs in the urban fringe, which began in 1960, and the increasing liberalization of the minimum population size requirements for CDPs, mark a continuing local involvement and interest in these geographic entities. In 1980, the Census Bureau delineated CDPs in the UAs of the six New England States (no CDPs had been delineated in New England UAs previously). For 1990, the change of the designation central city to central place further underlined the importance of CDPs in UA delineations.

Before each decennial census, the Census Bureau reviews the criteria for delineating UAs and extended cities. As a result of this review, the Census Bureau historically has proposed improvements to assure that these entities consistently measure the Nation’s settlement pattern. The Census Bureau then publishes the proposed criteria in the Federal Register and solicits comments from the data-using public. Where necessary, further revisions are made before the final criteria are published. For 1990, the following major changes were made:
 * Through the 1980 census, the urbanized area delineation process had taken place only once every decade, at the time of the decennial census. Beginning in 1986, the Census Bureau allowed the delineation of new UAs on the basis of a special census taken in the intercensal period. Two areas (Davis, CA, and Merced, CA) qualified as UAs on the basis of a special census; two others (Bowling Green, KY, and Elizabethtown–Radcliffe, KY) did not.
 * Areas that had been UAs in a previous census were not automatically grandfathered if their 1990 population fell below 50,000. As a result, two areas that had been UAs in 1980 (Danville, IL, and Enid, OK) were no longer UAs in 1990. 12-6Urban and Rural Classifications