1. Associate Professor, School of Geography, Geomatics and Planning, Jiangsu Normal Univ., No. 101, Shanghai Rd., Xuzhou, Jiangsu 221116, China (corresponding author).
2. Postgraduate Student, School of Geography, Geomatics and Planning, Jiangsu Normal Univ., No. 101, Shanghai Rd., Xuzhou, Jiangsu 221116, China.