Census & Metropolitan Definitions. Arthur C. Nelson, Ph.D., FAICP Presidential Professor & Director Metropolitan Research Center January 2010. Census Building Blocks. Census Tracts Census Blocks Census Block Groups County Subdivisions Traffic Analysis Zones. Census Tracts.
Arthur C. Nelson, Ph.D., FAICP
Presidential Professor & Director
Metropolitan Research Center
Small, permanent county statistical subdivisions.
Census tract boundaries normally follow visible features, but may follow governmental unit boundaries and other non-visible features, and they always nest within counties.
Census tracts designed to be relatively homogenous units with respect to population characteristics, economic status, and living conditions of creation.
They usually contain 1,500 to 8,000 people and average about four block groups.
There are about 66,000 tracts nationwide.
Census Blocks are the smallest entity for which the Census Bureau collects and tabulates census information (SF 1 only).
There are about 8.5 million blocks nationwide.
Block Groups are a combination of census blocks and are also a subdivision of census tracts.
Block groups generally contain between 600 and 3000 people and are made up of on average 40 census blocks.
There are about 211,000 block groups nationwide.
A TAZ is a special area delineated by state and/or local transportation officials for tabulating traffic-related data and usually consists of one or more census blocks, block groups, or census tracts.
County subdivisions are the primary divisions of counties for the reporting of decennial census data.
Minor civil divisions (MCDs) are the primary governmental or administrative divisions of a county such as boroughs, towns, and townships.
Census county divisions (CCDs) established by the Census Bureau in 21 states where there are no legally established MCDs.