The reference area encompasses the territorial extent of an area projected in the flat. Depending on the focus of interest, it can be the entire territory of Germany, individual states (Länder), so-called Raumordnungsregionen, districts, municipalities or square raster cells of diverse size.
All classes of ground cover or land use in a designated area are viewed as subdivisions of the selected area. The total of these classes gives the so-called reference area (see Classification). Seas and shallow coastal waters are only included when they are specified as belonging to the administrative municipal area (exceptional cases).