The United States Geological Survey (USGS) took over responsibility for mapping the country in 1879 and has been the primary civilian mapping agency of the United States ever since. Now you can view this complete seamless series of maps on Thoos.
The best known USGS maps are those of the 7.5-minute, 1:24,000-scale quadrangle series. A scale of 1:25,000 is used for maps based on metric units (1 centimeter = 0.25 kilometer). The area portrayed on each sheet ranges from 64 square miles at latitude 30 degrees north to 49 square miles at latitude 49 degrees north. (Zoom in all the way to view 7.5 minute maps)
A scale of 1:24,000 allows considerable detail to be shown in the quadrangle areas. It takes about 57,000 maps to cover the conterminous 48 States, Hawaii, and territories.