HILLSHADE MAPS: A NEW WAY TO LOOK AT THE EARTH

Hillshade maps, derived from DEMs (digital elevation models), or DTMs (digital terrain models), are a new way to look at the Earth. They are created from digitized 7½ minute topographic quadrangle maps and can be processed and printed from the on-line database maintained by the U.S. Geological Survey. The quality of the maps vary depending on original source. The digitization process involves systematically moving across the topographic map row by row and estimating the elevation at intervals in accord with the 30x30 meter pixel dimension. These quadrangles can be assembled by township, county, state, or region at a predetermine scale. The end product is a black/white or falsely colored map showing relative relief based on elevation of the desired area, which can be rotated and tilted to any desired angle for viewing. The State of Kansas is used as an example here, which emphasizes the same features present on other maps, but are not as obvious. Especially interesting is the prominence of the feather-fine fracture system which seemingly penetrates all of the geologic units exposed on the surface from Mississippian limestone in the southeast to the loess covering High Plains in western Kansas. The drainage pattern also focuses attention on major structural features such as the linear fracture/fault pattern. The circular or oval-shaped features, if negatively shaped, may represent solution features, impact craters, wind-fashioned, or animal created depressions, or if positive in shape, may be the reflection of the subsurface structure or configuration and pattern of features of the Precambrian basement.