Clemens, Corinna, and Ariane Clemens. “Peripheries, Boundaries, Transition Zones: Boundaries and Borders As a Basis for Spatial Planning Around Cities”. Raumforschung und Raumordnung | Spatial Research and Planning 57, no. 5-6 (September 30, 1999): 350–358. Accessed May 2, 2024. https://rur.oekom.de/index.php/rur/article/view/1103.