Geological Map 1 : 25,000 (Historical GK25) 1937
For the North German Plain made up of loose rock, and thus also for the entire State of Brandenburg including Berlin, the Geological Map at a scale of 1 : 25,000 (GK25) is a map of the geological (rock) formations exposed at the surface with a depth of representation of the geological conditions up to 2 m below the surface. It is the basic map for all geological issues and all derived maps that build on it (LBGR 2017).
From 1874 to 1939, the Prussian Geological State Institute carried out the first complete geological survey of the area of the present State of Brandenburg, including the sheets of the GK25 that relate to Berlin. 230 sheets were recorded geologically, and until around 1924 geologically-agronomically, and were published beginning in 1875 in installments of 3 to 9 sheets each. The area of the present State of Berlin was mapped in the years 1875 to 1883. Further revisions, usually the second edition, appeared in the years 1899 to 1937.
This set of maps, some of which are more than 100 years old, is still highly significant for use in the areas of geoscientific analysis as well as nature and soil protection. This is due on the one hand to the fact that a current set of maps is not available at a scale of 1 : 25,000. While the Geological Outline of Berlin at a scale of 1 : 50,000 is more up to date, it does not nearly measure up to the Historical GK25 with respect to detail (Limberg 1995, Lippstreu 2003).
Moreover, as the region was not very urbanised at the time, the maps allow structures and sites — mostly Holocene, i.e. postglacial — to be read off that were removed in the course of the subsequent urban development. Pools and wetlands from bog and half-bog formations or dunes were reshaped, cleared or filled. The information from the GK25 provides indications of structures that no longer exist, and this knowledge might be of interest for future projects of rewetting peatlands, restoring pools or renaturalising soils influenced by groundwater. Relationships in the landscape become apparent that in some cases have been invisible in the cityscape for decades.