Klaphake, Axel, and Jürgen Meyerhoff. “The Economic Value of Open Space in Urban Areas: An Application of the Contingent Valuation to an Urban Park in Berlin”. Raumforschung Und Raumordnung | Spatial Research and Planning, vol. 61, no. 1-2, Jan. 2003, pp. 107–117, https://doi.org/10.1007/BF03183079.