1. School of Geographic and Biologic Information, Nanjing University of Posts and Telecommunications, Nanjing 210023, China
2. Key Laboratory of Virtual Geographic Environment, Ministry of Education, Nanjing Normal University, Nanjing 210023, China
3. Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, Nanjing 210023, China
4. College of Geographical Science, Nanjing Normal University, Nanjing 210023, China