1. Lecturer, Centre for Spatial Information Science, School of Geography and Environmental Studies, Univ. of Tasmania, Private Bag 76, Hobart, Australia 7001.
2. Engineer, Jenkins & Potter, Consulting Engineers, 1st Floor, 67-74 Saffron Hill, London EC1N 8QX, U.K.
3. Professor, School of Geography and Environmental Studies, Univ. of Tasmania, Private Bag 78, Hobart 7001, Australia.