E. Oele, W. Apon, M. M. Fischer, R. Hoogendoorn, C. S. Mesdag, E. F. J. de Mulder, B. Overzee, A. Sesoren, & W. E. Westerhoff. (1983). Surveying the Netherlands: sampling techniques, maps and their application. Netherlands Journal of Geosciences, 355-372. Retrieved from https://njgjournal.nl/index.php/njg/article/view/13396