1. School of Public Administration and Law, Northeast Agricultural University, Harbin 150030, China
2. School of Economics and Management, Northeast Agricultural University, Harbin 150030, China
3. Department of Economics, Cheikh Hamidou Kane University, Dakar 15126, Senegal
4. Department of Geography, Cheikh Anta Diop University, Dakar P.O. Box 5003, Senegal
5. Department of Geography, UFR Sciences and Technologies, Assane Seck University, Ziguinchor P.O. Box 523, Senegal