Ritter, Ernst-Hasso, and Dietmar Scholich. “Regional Planning at Federal, State and Inter-Authority Levels: Selected Research Findings of the Academy for Regional Research and Regional Planning”. Raumforschung Und Raumordnung | Spatial Research and Planning, vol. 57, no. 2-3, Mar. 1999, pp. 155–167, https://doi.org/10.1007/BF03184485.