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 The 1990 UA delineation operation involved an examination of 635 potential UAs, including all or parts of 1,155 counties. These included all previous UAs, those that had qualified on the basis of a special census in the 1980s, all areas that had failed to qualify in 1980, and new areas that might qualify for the first time in 1990. Because of the extensive geographic scope of the operation, and because of the lengthy, labor-intensive nature of UA delineation work, the Census Bureau automated much of the task by using the TIGER data base and customized UA delineation software.

The 1980 UA boundaries were digitized and inserted into the TIGER data base, as were all representations of 1980 nonresidential urban land use, jumps, and undevelopable territory. For population concentrations that were not UAs in 1980, the Census Bureau digitized the boundaries of the central place(s) to serve as a starting point for making the 1990 UA determinations. Potential extended cities also were identified.

To perform the UA delineations, the Census Bureau developed interactive software that featured a visual screen display of census block densities from which small-area units were created. The software could display an entire UA, sometimes involving as many as five counties, on an interactive graphics terminal. Other advantages of the UA delineation software were its ability to: In addition, the software made it possible to perform numerous edits for consistency and completeness, and, ultimately, to assign the appropriate urban or rural classification code to each block in the TIGER data base. Urban and Rural Classifications12-15
 * Display area and density tables.
 * Plot line features.
 * Display nonresidential urban land use.
 * Measure both road and straight-line distances.
 * AggregrateAggregate [sic] census blocks for analysis.