How are the TIGER/Line Shapefiles organized?
The shapefiles are generally organized based on the Census Bureaus hierarchical relationship of geographic entities (see diagram in [PDF] format or a [TEXT] description). Entities that are defined independently from states and counties, such as ZIP Code Tabulation Areas, are available in nation-based shapefiles that encompass the entire country. Entities such as school districts and congressional districts that are defined within states but can cross county boundaries are represented in state-based shapefiles (i.e. one shapefile for each state). Entities that are defined within counties and do not cross county or state lines (such as Traffic Analysis Zones) are represented in county-based shapefiles. Beginning with the 2008 version, some geographies are available in multiple shapefiles. For example, census tracts are available in both county- and state-based shapefiles. This differs from the TIGER/Line files, which were available exclusively in county-based files. For more details abou
Geographic entities included in the Census Bureau’s tabulations are generally hierarchical. The organizational structure of the TIGER/Line Shapefiles is based on this hierarchical framework (see diagram in [PDF] format or a [TEXT] description). Shapefiles are released in up to four types of hierarchical coverages: American Indian Area-based, nation-based, state-based, and county-based. Some shapefiles are released in multiple coverages to increase flexibility of use. For more details about the most recent version of the files, see http://www.census.gov/geo/www/tiger/tgrshp2010/documentation.html.
