1. Davis, K., World urbanization 1950-70, Vol.1: basic data for cities, countries and regions, Population monograph series No.4, Berkely, 1969, pp. 10–20.
2. Typologie van de Nederlandse gemeenten naar urbanisatie graad, 31 mei 1960, C.B.S., Zeist, 1964.
3. Berry, B.J.L. and W.L. Garrison, The functional bases of the central place hierarchy, Economic Geography, 1958, Vol. 34, No. 2, pp. 145–154.
4. Davis, K., op.cit. 1, p.9, see table 1.
5. Van Hulten, M.H.M., Plan and reality in the IJsselmeer polders, Tijdschriftvoor Economische en Sociale Geografie, 1969, Vol.40, No.2, pp.67–76.