The smallest area for which complete-count census data are reported. Blocks are delimited by visible physical features such as streets or streams, or by invisible political lines such as city or county boundaries. Blocks are identified by a four-digit code that is new in 2000. Block Groups are a collection of blocks that begin with the same first digit. These are the smallest areas for which all census data including complete-count and sample are reported.
Tracts are small, statistical county subdivisions.
Local committees usually delineate the boundaries to represent relatively homogeneous neighborhoods and to maintain stable areas. Census tracts have about 2,500 to 8,000 residents. DMAs are revised annually. Current definitions represent the 2000-2001 series. Defined by self-identification, Hispanic origin refers to ethnicity, not race.