Terfrüchte, Thomas, et al. “Empirical Foundation of Central-Place-Concepts – Recommendations for an Ideal Type Approach”. Raumforschung Und Raumordnung | Spatial Research and Planning, vol. 75, no. 5, Oct. 2017, pp. 471–485, https://doi.org/10.1007/s13147-017-0505-0.