Baumheier, Ralph. “Co-Operative Planning of Settlements and Open Spaces in the ‘Regio Unterweser’: A New Approach to Cross-Border Co-Operation in the Area Bremen Lower Saxony”. Raumforschung Und Raumordnung | Spatial Research and Planning, vol. 58, no. 4, July 2000, pp. 337–342, https://doi.org/10.1007/BF03183799.