A subdivision of a census tract (or, in 1990, a block numbering area), a block group is the smallest geographic unit for which the Census Bureau tabulates sample data. A block group consists of the blocks within a census tract with the same initial di git. For example, block group 3 consists of all blocks within a 2000 census tract numbering from 3001 to 3999. In 1990, block group 3 consisted of all blocks numbered from 301 to 399Z.