@article{Longxu YAN_1576, author = {YAN Longxu, WANG De, ZHANG Shangwu}, title = {Theoretical foundation and framework for understanding urban centers}, publisher = {PROGRESS IN GEOGRAPHY}, year = {2020}, journal = {PROGRESS IN GEOGRAPHY}, volume = {39}, number = {9}, eid = {1576}, pages = {1576-1586}, keywords = {;urban centers system;theoretical framework;spatial competition;spatial connection;semi-lattice}, doi = https://www.progressingeography.com/EN/10.18306/dlkxjz.2020.09.014 }