Description: Census units are represented through a three tier hierarchical construction - census tracts, census block groups and census blocks. Census tracts are statistical subdivisions of a jurisdiction or census place each of which represents a population of approximately 4,000. Census block groups are subdivisions of census tracts averaging 900 inhabitants. Census blocks are subdivisions of census block groups and are usually defined as the smallest area bounded on all sides by streets. Block group numbers and block numbers will be repeated in different tracts.