1. Department of Geography and Geographic Information Science, University of Illinois at Urbana-Champaign, Urbana, IL, USA
2. Department of Geography and Resource Management, Institute of Space and Earth Information Science, The Chinese University of Hong Kong, Hong Kong, China
3. Department of Human Geography and Spatial Planning, Utrecht University, Utrecht, The Netherlands
4. Institute for Social Research and School of Information, University of Michigan, Ann Arbor, MI, USA
5. Center for Geographic Analysis, Institute for Quantitative Social Science, Harvard University, Cambridge, MA, USA