1. Key laboratory of Virtual Geographic Environment, Ministry of Education; Nanjing Normal University; Nanjing 210023 China
2. State Key Laboratory Cultivation Base of Geographical Environment Evolution (Jiangsu Province); Nanjing 210023 China
3. Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application; Nanjing 210023 China
4. Department of Geoinformatics - Z_GIS; University of Salzburg; Salzburg 5020 Austria
5. Department of Geography; University of Wisconsin-Madison; Madison USA