1. Jiangsu Provincial Key Laboratory of Geographic Information Science and Technology; Nanjing University; Nanjing 210093 China
2. Urban and Regional Research Centre Utrecht, Faculty of Geosciences; Utrecht University; Utrecht 3584 CS The Netherlands
3. Geoinformatics; Royal Institute of Technology; 10044 Stockholm Sweden
4. State Key Laboratory of Resources and Environmental Information System; Institute of Geographic Sciences and Natural Resources Research; Beijing 100101 China