USGS mapzones

Political

United States Department of Commerce

Website

United States Census Bureau

Website
Data Links
Census Maps and Data
Topologically Integrated Geographic Encoding and Referencing(TIGER) Products
TIGER/Line Shapefiles
Cartographic Boundary Shapefiles
FTP Directory
United States Open Data Catalog
Shapefiles
State Boundaries 500K
State Boundaries 5 m
State Boundaries 20m
United States Boundary 5m
United States Boundary 20m
Congressional Districts (115th Congress) 500K
Congressional Districts (115th Congress) 5m
Congressional Districts (115th Congress) 20m
Counties 500k
Counties 5m
Counties 20m
Primary Roads

United States Geological Survey

Website
Data Links
Water Resources
Water Watch
Data and Tools
Mapping, Remote Sensing and Geospatial Data
StreamStats v4 Batch Processing Tool
Data Catalog
Watershed Boundary Dataset
Hydrography
The National Map

United States Department of Agriculture

Website

Agricultural Research Service

Website
Data Links
Data Sets
National Agricultural Library