Delineation of City Regions Based on Commuting Interrelations: The Example of Large Cities in Germany

The comparison of cities with regard to their economic or demographic development may yield misleading results, if solely the cities in their administrative borders are the object of consideration. Frequently, historical borders of cities neither conform to the contemporary settlement structures, nor do they consider the mutual dependencies between cities and parts of their hinterland. Therefore, it is often claimed to use city regions as objects of comparison or for the sake of urban planning. Commonly, the delineation of functional regions is based on commuting flows from the municipalities in the hinterland of the core cities directed to the cores. A municipality is regarded as belonging to a certain city region if the share of out-commuters from this municipality to the respective core in the total mass of those employees who reside in that municipality is the largest one, and if this share exceeds a certain threshold value. However, commuting flows in the opposite direction are not considered. The method presented here delineates city regions on the base of bidirectional commuting flows. Hereby, various modifications regarding the characteristics of the employment base, the possibility of overlaps of regions, the formation of polycentric city regions, and of the minimum threshold value of mutual connectivity are applied to the sample of 81 German cities with more than 100 000 inhabitants. Finally, the effects of different kinds of regionalisation on the coefficients of regional specialisation of these cities and city regions are demonstrated.