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A census block is the smallest geographic unit used by the United States Census Bureau for tabulation of 100-percent data (data collected from all houses, rather than a sample of houses). The number of blocks in the United States, including Puerto Rico, for the 2010 Census was 11,155,486.Census blocks are grouped into block groups, which are grouped into census tracts. There are on average about 39 blocks per block group. Blocks typically have a four-digit number; the first number indicates which block group the block is in. For example, census block 3019 would be in block group 3.Blocks are typically bounded by streets, roads or creeks. In cities, a census block may correspond to a city block, but in rural areas where there are fewer roads, blocks may be limited by other features. The population of a census block varies greatly. As of the 2010 census, there were 4,871,270 blocks with a reported population of zero, while a block that is entirely occupied by an apartment complex might have several hundred inhabitants.Census blocks covering the entire country were introduced with the 1990 census. Before that, back to the 1940 census, only selected areas were divided into blocks.Census blocks are maintained within the Administration Feature and is dissolved out weekly.Administration is a polygon feature consisting of the smallest statistical areas bounded by visible features such as roads, streams, railroad tracks, and mountain ridges, as well as by nonvisible boundaries such as jurisdictional limits, school district, public safety boundaries, voting precincts, and census blocks. This methodology allows for single stream editing to move coincidental boundaries across many aggregate datasets simultaneously. Administration is maintained though an ArcGIS topology class in conjunction with County Parcels and Zoning. The topology prevents self-intersection and gaps, while ensuring complete coverage amongst the participating features. |