1. Alexander Woestenburg is a scientist and adviser at TNO – Strategy and Policy, Anna van Buerenplein 1, The Hague, NL-2595 DA; Erwin van der Krabben is Professor of Urban Planning and Property Development at Radboud University Nijmegen, PO Box 9108, Nijmegen 6500 HK, Netherlands; Tejo Spit is Professor of Urban and Regional Planning at the University of Utrecht, Faculty of Geosciences, Heidelberglaan 2, Utrecht 3584 CS, Netherlands;