1. Geological Survey of Canada, Natural Resources Canada, Ottawa, ON, Canada. E-mail: boyan.brodaric@canada.ca
2. National Center for Geographic Information and Analysis (NCGIA), School of Computing and Information Sciences, University of Maine, Orono, ME, USA. E-mail: torsten@spatial.maine.edu
3. Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON, Canada. E-mail: gruninger@mie.utoronto.ca