1. Christoph Alfken, Regionalverband Ruhr, Kronprinzenstraße 6, D-45128 Essen, Germany
2. Daniel Vossen, Institute of Economic and Cultural Geography, Leibniz Universität Hannover, Schneiderberg 50, D-30167 Hannover, Germany
3. *Korrespondierender Autor: Rolf Sternberg, Institute of Economic and Cultural Geography, Leibniz Universität Hannover, Schneiderberg 50, D-30167 Hannover, Germany