Christiaan van Paassen, The philosophy of geography: from Vidal to Hägerstrand, in Pred 1981, pp. 17–29 Pred, Allan, ed. (1981). Space and time in geography: essays dedicated to Torsten Hägerstrand. Lund: CWK Gleerup. ISBN978-91-40-30603-6. OCLC10145474.