The Census Bureau did not automatically recognize previously existing UA territory as part of the Census 2000 UA delineation process. There was no "grandfathering" of areas that qualified based on the results of earlier censuses.
For Census 2000, the Census Bureau used the territory designated as UCs, rather than the entity of places that have a specified population, to determine the total urban population outside of UAs. Previously, place boundaries generally were used to determine the urban or rural classification of territory outside of UAs. With the creation of UCs, place boundaries became "invisible" when creating and classifying the cores of densely settled population agglomerations.
Technological advances in the field of geographic information systems (GIS) during the last 10 years allowed the Census Bureau to automate the urban and rural delineation process for the first time in Census Bureau history.
The extended city criteria were modified extensively for Census 2000. Any place that is split by a UA or UC boundary is referred to as an extended place. Previously, the extended city criteria included only sparsely settled territory within incorporated places and relied on density and area measurements to determine whether or not portions of an incorporated place were excluded from the UA. The new urban area criteria, based solely on the population density of census Block Groups (BGs) and census blocks, provide a continuum of urban areas for Census 2000.
The Census 2000 criteria increased the allowable jump distance from 1.5 to 2.5 miles. The increase in the jump distance was proposed as a means to recognize improvements in the transportation network, and the associated changes in development patterns that reflect these improvements, coupled with governmental influence to provide additional "green space" between developments.
The Census Bureau developed the concept of "hops" to extend the urban definition across small nonqualifying census blocks, and thereby avoid the need to designate the break in qualifying blocks as a jump. Hops between qualifying areas are less than or equal to 0.5 mile.
For Census 2000, the area of an indentation in qualifying territory had to be four times the area of a circle with a diameter equal to the closure line of the indentation for the territory to be included in a UA or UC. Previously, an indentation only had to be two times longer than the distance across the mouth. The new criteria enabled the Census Bureau to use an automated methodology that reduced the chances of incorrectly classifying as urban, sparsely settled territory along the fringe of a core.
The uninhabitable jump criteria were revised for Census 2000 to be more restrictive regarding the types of terrain over which an uninhabitable jump could be made. For Census 2000 only water, military reservations, national parks, and qualifying floodplains were deemed to be "exempted territory," which replaced undevelopable as the term applied to these areas.
The UA central place and title criteria no longer follow standards predefined by other federal agencies. Previously, many UA central places and titles were based on metropolitan area (MA) central city definitions set forth by the Office of Management and Budget.
The new MA criteria will be, and always have been, applied later than the UA criteria. To avoid creating a situation in which the 2000 UA or UC central places and titles would need to follow MA central city definitions that were established in the early 1990s, the Census 2000 criteria create an objective, zero-based approach.