Breidenbach, P. et al. 2013. Staying Alone or Reaching more Success Together? A Path for more Regional Cooperation in the Ruhrgebiet. Raumforschung und Raumordnung | Spatial Research and Planning. 71, 2 (Apr. 2013), 143–156. DOI:https://doi.org/10.1007/s13147-013-0219-x.