1. Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, Nanjing, China
2. School of Geography and Ocean Science, Nanjing University, Nanjing, China
3. Key Laboratory of Virtual Geographic Environment (Nanjing Normal University), Ministry of Education, Nanjing, China
4. School of Geography, Nanjing Normal University, Nanjing, China
5. State Key Laboratory of Resources and Environmental Information System, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China
6. Department of Geography, University of Wisconsin-Madison, Madison, WI, USA