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 In conjunction with the 1980 census, the Census Bureau produced land area data for States; counties; places with a population of 2,500 or more; MCDs of 2,500 or more in 11 States (Connecticut, Maine, Massachusetts, Michigan, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and Wisconsin); metropolitan areas; urbanized areas; and postcensal congressional districts. (The Census Bureau did not produce area measurement data for small-area geographic entities such as census tracts, block groups, and census blocks.) The 1980 population census reports included land area data for places to tenths of a square mile and tenths of a square kilometer; for all other entities, the area figures were rounded to whole square miles and square kilometers.

For the 1990 census, the Census Bureau created the TIGER (Topologically Integrated Geographic Encoding and Referencing) System, which included a nationwide digital geographic data base, to automate the mapping and related geographic activities required to support the Census Bureau’s census and survey programs. The Census Bureau calculated all areal values, for both land and water, from the specific set of boundaries recorded for each entity in the TIGER data base. As a result, there are four major differences between the 1990 census and previous ones regarding area measurements:
 * The values for the 1990 census area measurements are based on the information contained in a single, consistent geographic data base rather than on a variety of maps supplemented by historical and local information. The TIGER data base is based on the U.S. Geological Survey’s 1:100,000-scale maps for the coterminous 48 States, except for the areas covered by the GBF/DIME-Files, which are based on the MMS. The TIGER data base for Alaska, Hawaii, Puerto Rico, and the Outlying Areas reflects the results of manual digitizing outside GBF/DIME-File areas using primarily 1:24,000-, 1:63,360-, and 1:250,000-scale USGS maps for Alaska and 1:20,000-, 1:24,000-, and 1:25,000-scale maps for the other entities. By integrating these various map sources into a Notes and References 15-4Area Measurement/Water Classification