Abstract: The centrality of a city can be defined as several parameters such as its rank-size rule, the node connectivity in the network system, and the flow intensity of different network nodes. A combined study of the hierarchy structure of regional cities and their connected network is widely regarded as a feasible direction that remains to be explored in the field of the urban system theoretically and practically. 52 cities in the region of Yangtze River Delta were study subjects in this paper. Firstly, a pyramid structure can be found in the hierarchy system of cities through the establishment of a center city index which was used to measure the centrality of cities in the study. Meanwhile, the distribution of different hierarchy cities suggests a spatial trend for “circle development plus axis extension” in this area. Secondly, an analysis of the urban network system in Yangtze River region was conducted through dissecting the associative network of listed companies. As the result implied, a shifting from the traditional “Z”-shape to a “π”-shape was emerging in the distribution of cities with dominant positions in centrality. Also, a cross-administrative connection, along with a neighboring effect have both contributed to the formation of the current network system of cities. Therefore, the hierarchy system coexists with the connection network, together forming the two urban systems in the context of multiple organization modes of economic activities in cities. Based on a framework of hierarchy system-network analysis, this paper presented distinctive urban character through studying the synthetic relation combine the centrality of city hierarchy and nodality of city network of each city. Hence, the hierarchy and classification of major cities in this region have been achieved. Cities have been divided into 5 ranks and 7 types, including: one global city-Shanghai; three national cities-Hangzhou, Nanjing, Suzhou; six major cities in provincial level-Wenzhou and other five; eight network pivots in provincial level-Ningbo and other seven; eight major cities in sub-regional level-Yancheng and other seven; six network pivots in sub-regional level-Huaibei and other five; and other nineteen local cities. A further study on the guiding policy of cities’ classification in accordance with their types can be conducted in the future on the basis of the dividing method adopted in this paper. Several factors can be taken into consideration in such policy, including to improve the systematic openness of cities with relatively high centrality by promoting their infrastructure connectivity, extending the industrial chains and etc; as well as to advance the rank of network pivots by intensifying the resource agglomeration effects, and improving their services.
Key words：central city; hierarchy structure; city network; Yangtze River Delta Region