1. Franz-Benjamin Mocnik, Bremen Spatial Cognition Center, University of Bremen, P.O. Box 330 440, 28334 Bremen, Germany and Institute of Geography, Heidelberg University, 69120 Heidelberg, Germany
2. David Fairbairn, School of Civil Engineering and Geosciences, Newcastle University, Cassie Building, Newcastle upon Tyne, NE1 7RU, UK