1. School for Policy Studies, University of Bristol, 8 Priory Road, Bristol BS8 1TZ, England
2. Department of Geography, University of Sheffield, Sheffield S10 2TN, England
3. National Centre for Geocomputation, National University of Ireland Maynooth, Co. Kildare, Ireland
4. Peninsula College of Medicine and Dentistry, John Bull Building, Plymouth PL6 8BU, England