A Geological Map is a special purpose Map made to show Geological Features. Rock Units or Geologic Strata are shown by Colour or Symbols to indicate where they are exposed at the Surface. Bedding Planes and Structural Features such as Faults, Folds, Foliation's, and Lineation's are shown with Strike and Dip or Trend and Plunge Symbols which give these features' three dimensional orientations. Stratigraphic Contour Lines may be used to illustrate the surface of a selected Stratum illustrating the subsurface Topographic Trends of the Strata.