1. Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China
2. Center for Chinese Agricultural Policy, Chinese Academy of Sciences, Beijing 100101, China
3. University of Chinese Academy of Sciences, Beijing 100049, China
4. Leibniz Institute of Agricultural Development in Transition Economies (IAMO), Theodor-Lieser Street 2, 06120 Halle (Saale), Germany
5. College of Geomatics, Shandong University of Science and Technology, Qingdao, Shandong 266590, China