The concept demonstrated here, hill shading , shows the shape of the land by intensity of the Sun's shadows. This concept is not new. This map is a digital shaded-relief image . The gray tone of each square is a brightness value computed from a mathematical relation between ground slope and direction and the position of the observer and a simulated Sun.
Surface features contain clues to understanding the Earth.
Geologists search for the clues and decode them to learn about natural hazards and resources. This is the most detailed and accurate view of terrain for the entire U.S.yet put together. It resembles traditional perspective drawings, but contains much more information. The two contrast vividly in surface roughness, texture, structural and coastline patterns, and freshness of relief. The map is accompanied by a pamphlet explaining how image processing and computer graphics have automated the art of landscape portrayal.