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 are quite different. Patterns, sizes, and shapes of census blocks vary within and between areas. Factors that influence the overall configuration of census blocks include topography, the size and spacing of water features, the land survey system, and the extent, age, type, and density of urban and rural development.

The Census Bureau entirely automated the assignment of census block numbers for the 1990 census. The magnitude and complexity of the undertaking generally precluded major State or local involvement in the delineation of census block boundaries. Also, it was important to be consistent when adhering to census block number assignment guidelines. As part of the Census Bureau’s Redistricting Data Program (see, “Voting Districts,” for further information), the Census Bureau did allow State agencies to specify features that would be held as 1990 census block boundaries (must-hold features).

As part of the Census Block Definition Program, the Census Bureau also allowed the officials of American Indian reservations to identify must-hold features. Based on the stated goals of maximizing the number of census blocks within each BG, the Census Bureau developed a computer routine that analyzed the network of TIGER data base features that formed polygon areas within each 1990 BG and assigned a number to each. This eliminated the earlier problems of duplicate numbers, areas with no number assigned, and areas with multiple numbers assigned.

The program for assigning census block numbers gave major consideration to the type of feature, as well as the shape and minimum size of a potential census block:
 * The minimum size of a census block was 30,000 square feet (0.69 acre) for polygons bounded entirely by roads, or 40,000 square feet (0.92 acres) for other polygons. There was no maximum size for a census block.
 * Exceptions to the minimum polygon sizes were made where the polygon was entirely bounded by must-hold features that needed to be maintained as census block boundaries. 11-10Census Blocks and Block Groups