1. Department of Geography and Planning, University of Saskatchewan, Kirk Hall, 117 Science Place, Saskatoon, SK S7N 5C8, Canada;
2. College of Resources and Environment, Shanxi Agricultural University, No. 1 Mingxian South Road, Taigu, Shanxi, 030801, China;
3. College of Geomatics, Xi’an University of Science and Technology, No. 58 Yanta Road, Xi’an, Shaanxi, 710054, China