The data used to create the Visible and Elevation layers, as well as some of the high-resolution maps used in the Apollo layers, are courtesy of the U.S. Geological Survey.
Much of the rest of the material for the Apollo layer is derived from NASA's Apollo Lunar Surface Journal.
The USGS Geologic Atlas of the Moon, the Lunar Chart (LAC) Series, and some Apollo imagery are provided by the Lunar and Planetary Institute, managed by USRA.