G. T. A. Hof, R. Reiling, E. Zilverberg, and Th. W. M. Levelt. “An Areal Classification by Means of Cluster Analysis Using Abiotic Landscape Data”. Netherlands Journal of Geosciences (January 1, 1981): 427-432. Accessed April 3, 2026. https://njgjournal.nl/index.php/njg/article/view/13649.