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Census Tracts
Census tracts are relatively small geographies that generally have stable boundaries, into which metropolitan (and certain other) areas are divided for the purpose of providing statistics. When tracts are established, they are designed to be relatively homogeneous areas with respect to population characteristics, economic status and living conditions. A tract contains 4,000 people on average although the population of individual census tracts can vary widely from this average.
Tract boundaries are established cooperatively by local Census Statistical Area Committees and the Census Bureau, in accordance with guidelines that stress the need for visible boundaries. Geographic shape and size of tracts are of relatively minor importance. Tract boundaries are established with the intention of being maintained over a long period of time so that statistical comparisons can be made from Census-to-Census. They observe county lines and are defined to cover all of the territory within each tracted county.
Census tracts are unique within each county and are identified by a four-digit base code and a two-digit suffix (e.g., 4039.23). All valid census tract numbers are in the range 0001 to 9499.99. A .99 suffix identifies a census tract with a population entirely aboard civilian or military ships. Census tract numbers may be split for tabulation purposes by the boundaries of places, Minor Civil Divisions (MCDs) and Census County Divisions (CCDs). Many of the .70 to .98 suffixes identify sliver tracts that were created as part of the 1990 Census. Some of these sliver tracts have very small populations and land area. As such, the data has been summarized with an adjacent tract.