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This layer contains a unique geographic identifier (GEO_ID_BLK) for each block that is the key field for the data from censuses and surveys such as Decennial Census, Economic Census, American Community Survey, and the Population Estimates Program. Data from many of the Census Bureau’s surveys and censuses, are available at the Census Bureau’s public data dissemination website (https://data.census.gov/). All original TIGER/Line shapefiles and geodatabases with demographic data are available at<https://www.census.gov/geographies/mapping-files/time-series/geo/tiger-line-file.html>
The TIGER/Line Shapefiles are extracts of selected geographic and cartographic information from the Census Bureau's Master Address File (MAF)/Topologically Integrated Geographic Encoding and Referencing (TIGER) Database (MTDB). The shapefiles include information for the fifty states, the District of Columbia, Puerto Rico, and the Island areas (American Samoa, the Commonwealth of the Northern Mariana Islands, Guam, and the United States Virgin Islands). The shapefiles include polygon boundaries of geographic areas and features, linear features including roads and hydrography, and point features. These shapefiles do not contain any sensitive data or confidential data protected by Title 13 of the U.S.C.
Census blocks are statistical areas bounded on all sides by visible features such as streets, roads, streams, and railroad tracks, and by non-visible boundaries including city, town, and county boundaries. Generally, census blocks are small in area as a block in a city. However, Census blocks in suburban and rural areas may be large, irregular and bounded by a variety of features In remote areas, census blocks may encompass hundreds of square miles. Census Block Numbers—Census blocks are numbered uniquely within the boundaries of each state, county, census tract with a 4-character census block number. The first character of the tabulation block number identifies the block group. A block number can only be unique by using the decennial census state (STATEFP20), county (COUNTYFP20), census tract (TRACTCE20), and block (BLOCKCE20). The entire block number is the GEO_ID_BLK. There is no consistency in block numbers from census to census.
Full documentation: https://www2.census.gov/geo/pdfs/maps-data/data/tiger/tgrshp2020/TGRSHP2020_TechDoc.pdf