2.3.1 Geological mapping of coalfields
Coalfields can be divided into two categories: exposed coalfields, where the coal-bearing strata outcrop at the surface, and concealed coalfields, where they are hidden beneath younger rocks. Exposed coalfields can be defined with considerable precision by surface geological investigations; indeed geologists recording field data still represent the cheapest exploration 'tool' available to the coal industry.
In populated regions, the locations of coal outcrops are well known and mapped. However, in remote areas new finds are still possible. In such areas data acquired from satellites or aircraft are assessed before geologists start exploring on the ground. The Global Positioning System (GPS), now increasingly used for navigation, uses signals from satellites to pinpoint locations precisely, so that geologists can more easily create accurate maps in the field. Field data are increasingly processed using spatial analysis software to create digital maps of coal outcrops and to model the likely extension of the coal beneath the surface.