It is important that you understand what a geological map is as this will help you appreciate its need and best make use of it. Geological maps, as is the case with all maps, show where things are located. They are however, unlike other maps in that they do not show distribution of national boundaries, roads, rivers, and the likes, and they do not only show what is on the ground. Geological maps show geological features including folds, faults, rock structure, rivers, mountains, and valleys. Most geological maps are printed on top of regular maps or base maps. This helps you locate different places on a geological map. Base maps are usually light colored so that you are able to see geological features clearly.
A geological map is represented by lines, symbols, and colors. The colors are the most striking features in these maps. The different colors represent different geologic units, with a geologic unit being a volume of a particular rock in a particular age range. This means, as an example, that sandstone of a particular age might be orange while that of a different age might be pale brown. A geologic unit gets its name based on where it was first studied or where its characteristics are displayed prominently. Note that some of these units have not yet been named. Such units get their names based on the kind of rock like “undivided shale,” unnamed sandstone,” and “shale and sandstone.” The naming is done by the geologists who first studied the area. The redefining of these geologic units is commonplace as scientific advances in mapping technology manifest and the need for further investigation arise, and as a result of disagreements.
Geological strata is also shown using symbols. Structural features and bedding planes like folds, faults, lineations, and foliations are represented by trend & plunge or strike & dip symbols on a geological map. These symbols give the features their 3D orientations. The strata’s subsurface topographic trends can be illustrated using stratigraphic contour lines.
A geological map is important because it helps determine such things as the likelihood of earthquakes, floods, and other natural calamities and it helps in the detection of groundwater, mineral deposits, and other natural resources. Geological mapping helps in determining whether an area is suitable for agriculture or urban development and it helps policy makers determine the best place for such infrastructure as rail tracks and pipelines. You will notice differences in geological maps of different countries as well as maps in the same country (with regard to such things as the scale).