Mi Yan, Nanjing Normal University, Nanjing, China, Zhengyu Liu, The Ohio State University, Columbus, OH, United States, Liang Ning, Nanjing Normal University, School of Geography, Nanjing, China; University of Massachusetts Amherst, Amherst, United States and Jian Liu, Nanjing Normal University, School of Geographical Sciences, Nanjing, China