What are the base map services (or URLs) used in The National Map viewer?
The National Map viewer uses a series of composite base maps, which combine layers into tile cache services with the cartographic richness of multiple data sources. The following composite base maps are available:
USGS Topo - combines the most current data (Boundaries, Elevation, Geographic Names, Hydrography, Land Cover, Structures, and Transportation, and other themes) that make up The National Map. Contours generated for US Topo products are visible at 1:36,000 and 1:18,000 scales.
USGS ImageryOnly - combines imagery from the following sources: Blue Marble Next Generation from world scale through 1:1.2M; NAIP from 1:1M through 1:18K for the conterminous U.S.; high resolution orthoimagery for Hawaii; and Landsat from 1:1M to 1:72K for Alaska, Puerto Rico, and the Pacific Islands.
USGS ImageryTopo - combines imagery with Contours and other vector themes (Boundaries, Geographic Names, Hydrography, Structures, and Transportation), based on cartographic styling used on US Topo products.
Hydro-NHD - combines naturally occurring and constructed bodies of surface water (lakes, ponds, and reservoirs), paths through which water flows (canals, ditches, streams, and rivers), and related entities such as point (or point event) features (springs, wells, stream gages, and dams) from the National Hydrography Dataset (NHD).
Hill Shade - consists of shaded relief derived from 1/3 arc-second data from the 3D Elevation Program (3DEP), a seamless dataset of raster elevation data for the conterminous United States, Alaska, Hawaii, and U.S. Territorial Islands.
TNM Blank - consists of ocean tints and coastal shorelines to provide an outline of the United States as a blank base map for addition of other services.