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 operations that produced maps, created address reference files, and established various geographic code files for use in documenting geographic relationships at the time of each census and survey. Because all these types of geographic products were produced in separate clerical operations, there were errors, omissions, and inconsistencies that caused problems for field operations, other data collection and processing operations, and data users. This was particularly true in regard to the inventory of census blocks. At times, the clerical procedures used to assign numbers to census blocks and to revise other tabulation entities were out of phase with revisions to the census maps. There were instances where duplicate census block numbers were assigned within a single BG, or where census block numbers accidentally were removed from the maps. There was a need for a stable structure of census collection geography at the census block level. The development of the Topologically Integrated Geographic Encoding and Referencing (TIGER) System, an automated geographic data base, permitted the Census Bureau to delineate census blocks on a nationwide basis for the 1990 census.

The delineation of census blocks and BGs could not begin until the TIGER data base contained an updated system of physical features and geographic boundaries. The Census Bureau created the TIGER data base using raster-scanned images of the U. S. Geological Survey’s (USGS) 1:100,000-scale topographic maps. In the built-up metropolitan cores, the previous GBF/DIME-Files were reformatted and inserted into the new data base. The Census Bureau then updated this digital map base using current map sources, and added new features, street names, and address ranges. The digitized images from the 1:100,000-scale maps were vectorized, merged, and reformatted into whole county partitions. The Census Bureau inserted 1980 geographic boundaries, such as county, place, MCD, American Indian areas, census tracts, and BGs into the data base from two sources. For areas covered by GBF/DIME-Files, the Census Bureau transferred geographic entity boundary information from those files. For areas beyond GBF/DIME-File coverage, the Census Bureau inserted higher-level 1980 geographic information by digitizing the boundaries of 1980 BGs where BGs were the collection unit, 11-8Census Blocks and Block Groups