The depths to groundwater are calculated from the difference between surface heights and the height of the groundwater level above sea-level. The calculations of groundwater levels are based on data taken from approximately 1,500 groundwater measuring sites. The data was collected in May 1995, in cooperation with the State Water Utiliy of the Berlin Department of Urban Development, Environmental Protection and Technology, and the Brandenburg State Environmental Agency. For areas with confined groundwater, selected geological drillings of the Drilling Archive were used. The terrain elevations were taken from the Terrain Elevations Model in the Environmental Information System (UIS). The statistical base and methodology used for this model are described in the text accompanying Map 01.08.