What are the base map services (or URLs) used in The National Map?

The National Map Services offers a series of composite base maps that combine layers into tile cache services with the cartographic richness of multiple data sources. The following base maps are available:

• USGS Topo  - combines the most current data (boundaries, geographic names, transportation, elevation, hydrography, land cover, and other themes) that make up The National Map. Contours generated for the US Topo product are included and are visible along with other data to 1:9,000 zoom scale.
• USGS Shaded Relief - created using data from the 3D Elevation Program (3DEP), which maintains a seamless dataset of best available raster elevation data for the conterminous United States, Alaska, Hawaii, and Territorial Islands of the U.S.  
• USGS Imagery Only - combines imagery from the U.S.; resolution may vary from 6 inches to 1 meter. 
• USGS Imagery Topo - combines imagery with contours and other vector themes (boundaries, geographic names, hydrography, structures, and transportation), based on cartographic styling used on US Topo products. 
• Hydrography - combines naturally occurring and man-made bodies of surface water, paths through which water flows, and ​related features​ such as stream gages and dams​​, and additional hydrologic information​.

Learn more: The National Map Applications