1. School of Geographic Science, Nanjing Univ. of Information Science and Technology, Pukou District, Nanjing 210044, China.
2. Associate Professor, Dept. of Civil and Environmental Engineering, Portland State Univ., 1930 SW 4th Ave., Portland, OR 97201-5304 (corresponding author).
3. Professor, Spatial Information Research Centre of Fujian Province, Fuzhou Univ., Fuzhou 350002, China.
4. Professor, Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China.