Entities that are defined independently from states and counties, such as American Indian Areas, are available in nation-based shapefiles that encompass the entire country. Though defined within states, county boundaries are available in nation-based as well as state-based shapefiles. The following layers are included:

American Indian/Alaska Native/Native Hawaiian Area (Census 2000 and current)
American Indian Tribal Subdivision (Census 2000 and current)
County and Equivalent (Census 2000 and current)
Combined New England City and Town Area (current)
Combined Statistical Area (current)
Metropolitan Division (current)
Metropolitan/Micropolitan Statistical Area (current)
New England City and Town Area (current)
New England City and Town Area Division (current)
State and Equivalent (Census 2000, current, and Economic Census)
Urban Areas (Census 2000 and corrected Census 2000)
3-Digit ZIP Code Tabulation Area (Census 2000 and 2002)
5-Digit ZIP Code Tabulation Area (Census 2000 and 2002)
Military Installation (current)

American Indian Area-Based Files

The following layers are available by American Indian Area:

American Indian Tribal Subdivision (Census 2000 and current)

State-Based Files

Entities such as school districts and congressional districts that are defined within states and can cross county boundaries are represented in state-based shapefiles. Though defined within counties, blocks, block groups, census tracts, and county subdivisions are available in state-based as well as county-based shapefiles. Though defined within states, counties are available in state-based as well as nation-based shapefiles. The following layers are included:

Alaska Native Regional Corporation (Census 2000 and current)
Block (Census 2000 and current)
Block Group (Census 2000)
Census Tract (Census 2000)
Commercial Region (Economic Census)
110th Congressional District (Congress elected in 2006)
108th Congressional District (Congress elected in 2002)
Consolidated City (Census 2000, current, and Economic Census)
County and Equivalent (Census 2000, current, and Economic Census)
County Subdivision (Census 2000 and current)
Place (Census 2000, current, and Economic Census)
1-Percent Public Use Microdata Area (Census 2000)
5- or 10-Percent Public Use Microdata Area (Census 2000)
Elementary School District (Census 2000 and current)
Secondary School District (Census 2000 and current)
Unified School District (Census 2000 and current)
State Legislative District—Lower Chamber (Census 2000 and current)
State Legislative District—Upper Chamber (Census 2000 and current)
Urban Growth Area (Census 2000 and current)

County-Based Files

Entities that are defined within counties and do not cross county or state lines such as census tracts and voting districts are represented in county-based shapefiles. Though defined within counties, blocks, block groups, census tracts, and county subdivisions are available in state-based as well as county-based shapefiles. The following layers are included: