In 1933 the geographer Walter Christaller published his dissertation Die zentralen Orte in Süddeutschland, the central places in southern Germany. It described towns as a hierarchy of central places, each serving the area around it. In 1968 the conference of ministers for spatial planning fixed a hierarchy for the whole country with four levels: upper, middle, lower and small centers.
The concept is now in federal law. Section 2 of the Spatial Planning Act says that settlement ist vorrangig auf vorhandene Siedlungen mit ausreichender Infrastruktur und auf Zentrale Orte auszurichten, is to be directed first to existing settlements with sufficient infrastructure and to central places. Die soziale Infrastruktur ist vorrangig in Zentralen Orten zu bündeln. Social infrastructure is to be concentrated mainly in central places.