You can search the National Archives Catalog to find descriptions and digitized images of historical maps and cartographic data files as well as documents and photographs related to geography.
New Fortification Index Available Online
RG 407: WWII Records Now Fully Digitized and Available Online
RG 241: Restored Patents Now Fully Digitized and Available Online
Record Group 26: Records of the U.S. Coast Guard, Series: Lighthouse Plans and Maps, 1793 - 1939
Record Group 145: Records of the Farm Service Agency,
Indexes to Aerial Photographs of the United States, 1953 - 1957