1. a School of Environmental Science, Nanjing Xiaozhuang University, Nanjing, Jiangsu 211171, China
2. b Key Laboratory of Virtual Geographic Environment (Nanjing Normal University), Ministry of Education, Nanjing, Jiangsu 210023, China
3. c Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, Nanjing 210023, China