Koitka, Heike. “Working Together to Develop Indicators! A New Module for Successful Regional AGENDA 21 Processes: Interim Results from the Märkischer Kreis Region”. Raumforschung Und Raumordnung | Spatial Research and Planning, vol. 58, no. 6, Nov. 2000, pp. 488–498, https://doi.org/10.1007/BF03182994.