Affiliation: | a Department of Geomatics, University of Melbourne, Vic. 3010, Australia b Department of Computer Science, Keele University, Staffs ST5 5BG, UK c Department of Earth Sciences and Geography, Keele University, Staffs ST5 5BG, UK d NCGIA, University of Maine, Boardman Hall, Orono, ME 04469-5711, USA |