Information System (LREIS), the Institute of Geographic Sciences and Natural Resources Research (IGSNRR), the Chinese Academy of Sciences; the University of Chinese Academy of Sciences (UCAS) in Beijing, China; and the Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application in Nanjing, China. Hui-Ran Gao is a graduate student at the LREIS, the IGSNRR, the Chinese Academy of Sciences; and the UCAS in Beijing, China. Liang-Jun Zhu (corresponding author) is a doctoral student at the LREIS, the IGSNRR, the Chinese Academy of Sciences; and the UCAS in Beijing, China. AXing Zhu is a professor at the Key Laboratory of Virtual Geographic Environment (VGE),
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