Although it looks like a satellite photograph, this image (56”x36”) was created by computer processing over 12 million elevation points, taken from topographic maps, to resemble a sunlit surface. It portrays clearly not only large, obvious features, such as the Appalachian Mountains, but also smaller or more subtle feature, like the fine-grained hummocky texture of the Nebraska Sand Hills. The tone of the image is equivalent to terrain roughness: steep slopes are black and white, gentle slopes are gray. A legend booklet accompanies the map.-(From the USGS description)- Scale 1:3,500.000. By Gail P. Thelin and Richard J. Pike, 1991.