1. Institute of Remote Sensing and Geographical Information Systems, School of Earth and Space Sciences, Peking University, Beijing, China
2. CyberGIS Center for Advanced Digital and Spatial Studies, Department of Geography and Geographic Information Science, University of Illinois at Urbana-Champaign, Urbana, IL, USA
3. School of Geosciences and Info-Physics, Central South University, Changsha, Hunan, China