1. School of Geography and Ocean Science, Nanjing University, Nanjing 210023, China
2. Jiangsu Provincial Key Laboratory of Geographic Information Science and Technology, Nanjing 210023, China
3. Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, Nanjing 210023, China
4. Max Planck Institute for Demographic Research, Konrad- Zuse-Str. 1, 18057 Rostock, Germany
5. Leverhulme Centre for Demographic Science and Department of Sociology, University of Oxford, Oxford OX1 1JD, UK
6. Department of Agricultural Economics, Sociology, and Education, Pennsylvania State University, University Park, PA 16802, USA