1. Department of Spatial Planning and Environment, Faculty of Spatial Sciences, University of Groningen, P.O. Box 800, 9700 AV Groningen, Netherlands.
2. UK Clinical Research Collaboration Centre for Diet and Activity Research and Medical Research Council Epidemiology Unit, School of Clinical Medicine, University of Cambridge, Box 285, Cambridge Biomedical Campus, Cambridge CB2 0GG, United Kingdom.
3. Department of Technology, Policy, and Management, Delft University of Technology, 2628 BX Delft, Netherlands.