1. Department of Geography, University of Western Ontario, Social Science Centre,
London, Ontario, N6A 5C2, Canada,
2. Department of Sociology, University of Toronto, 725 Spadina Avenue, Toronto,
Ontario, M5S 1A1, Canada,
3. Department of Civil Engineering, Universidad de Concepcion, Edmundo Larenas s/n,
Concepcion, PO Box 160-C, Chile,