Topographic and Surface Geologic Maps

Topographic contour maps show the configuration of the earth’s surface and are constructed by studying the variations in slopes, streams, cliffs, hilltops, etc., using stereoaerial photographs and satellite imaginary. A topographic map, which is a graphic representation of a portion of the earth’s surface is constructed at a specific scale, and represents a top or surficial view of the landscape whereas a profile or cross section is constructed through certain critical points across a straight line on a map. Two types of topographic maps are usually prepared for field investigations: a regional base map and a detailed site map. The regional base map is used for location and general features and can be easily obtained from published sources and used directly for illustrative purposes. The site specific topographic map may contain o.61 to 1.22 m contour intervals depending on the details required. U.S. Geologic Survey maps (USGS) (7.5-minute quadrangles) have contour intervals of 3 m or more.