Obtaining data for a geologic map from field geology involves many tasks including photo interpretation, field checking, field data collection, drill hole interpretation, and geologic interpretation.
Geologic mapping is a highly subjective science.
The geologic data presented in a map are intended for non site-specific use. Determining the quality of geologic mapping is quite difficult but certainly the scale of the mapping is the single most important attribute. In addition, the emphasis of the geologic mapping affects what is portrayed on the map. Most geologic studies by individual geologists are quite limited in their areal extent. To have continuous geologic coverage over a large area, a geologic compilation is necessary.