In Finland the glasiofluvial formations, like sandy eskers and end morraines, are the most important storages of groundwater. Because of the growing risk of pollution, the mapping and protection of aquifers has become an important target of the environmental research. A typical survey area is usually large, e.g 40 km', so there is a need for regional prospecting. The Geological Survey of Finland (GTK) has developed an useful methodology which gives regional information of the bedrock topography and the thickness of overburden. It is based mainly on the gravity interpretations.