Rock units or strata are shown by colour or symbols which show where they are exposed at the surface. Three-dimensional features like faults, folds, with symbols which give these features' orientations.
Stratigraphic contour lines may be used to illustrate the surface of a selected strata illustrating the subsurface topographic trends of the strata. Isopach maps detail the variations in thickness of stratigraphic units. It is not always possible to show this properly: the strata may be extremely fractured, mixed, or otherwise disturbed. There are often gaps (discontinuities) where erosion has removed strata.
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Geological map Facts for Kids. Kiddle Encyclopedia.