Abstract: A census block group (BG) is a cluster of census blocks having the same first digit of their four-digit identifying numbers within a census tract. (See also Census Tract.) For example, block group 3 (BG 3) within a census tract includes all blocks numbered from 3000 to 3999. BGs generally contain between 600 and 3,000 people, with an optimum size of 1,500 people. Most BGs were delineated by local participants as part of the U.S. Census Bureau's Participant Statistical Areas Program. The U.S. Census Bureau delineated BGs only where a local, state, or tribal government declined to participate or where the U.S. Census Bureau could not identify a potential local or tribal participant. BGs never cross the boundaries of states, counties, or statistically equivalent entities, except for a BG delineated by American Indian tribal authorities, and then only when tabulated within the American Indian hierarchy. (See also Tribal Block Group.) BGs never cross the boundaries of census tracts, but may cross the boundary of any other geographic entity required as a census block boundary. In decennial census data tabulations, a BG may be split for statistical purposes for every unique combination of American Indian area, Alaska Native area, Hawaiian home land, congressional district, county subdivision, place, voting district, or other tabulation entity. For example, if BG 3 is partly in a city and partly outside the city, there are separate tabulated records for each portion of BG 3. BGs are used in tabulating data nationwide, as was done for the 1990 census, for all block-numbered areas in the 1980 census, and for selected areas in the 1970 census. For statistical purposes, BGs are a substitute for the enumeration districts (EDs) used for reporting data in many parts of the United States for the 1970 and 1980 censuses and in all areas before 1970. The cartographic boundary files are a generalized extract from the U.S. Census Bureau's TIGER database. Line simplification/smoothing was performed with a tolerance of 0.005 decimal degrees and a coordinate reduction using the Douglas-Peucker method with a tolerance of 0.0003 decimal degrees. Very small polygons were eliminated when the combination of geographic codes existed elsewhere. The geography was clipped back to the shoreline of the United States, in contrast to TIGER/Line¿¿¿¿¿¿ which shows the full extent of geography out to the 3-mile limit.
Purpose: These generalized cartographic boundary files are originally produced to support the spatial geographic infrastructure for certain mapping functions within the Census Bureau's American Fact Finder and in support of the LandView Geographic Data Viewer. The generalized files have a much smaller file size than the original file extraction from the Census Bureau's TIGER database, resulting in faster download and processing times.

Progress: Complete
Update Frequency: As needed

Theme Keywords: ISO 19115 Topic Categories, boundaries, None, Cartographic, Boundary, generalized, government, boundaries, statistical, Block Group, census block, census block group, FGDC Framework Themes, FWGOVERNMENTALUNITS
Place Keywords: United States, State, Minnesota, 27

Access Constraints: None
Usage Constraints: The boundaries in this file are for statistical purposes only. They do not represent legal boundaries.