1. A correction to gravity data required because the surroundings are not all at the same elevation as the meter. Relief in the immediate vicinity of the station may require special surveying (terrain surveying), whereas corrections for more remote relief often are made from a topographic map using a terrain-correction template or zone chart. 2. A correction to seismic data because of the effect of topographic loading on velocity. 3. A correction to magnetic or electrical data because of terrain effects.