Isopach maps show the thickness of rocks or sediments. This is a type of contour map that shows the difference in rock or sediment thickness compared to the distance. This type of map can be used for many different uses; including knowing where drilling would be the easiest. This is a lot like a topographic map, but instead of showing the difference in elevation, it shows the difference in the thickness of rocks. This map shows the area in New York and Pennsylvania and where the rock is the thickest.