Abstract:

Since the Reform and Opening Up, urban agglomerations have developed rapidly. However, issues in the developmental process such as destruction of the ecological environment and uncoordinated internal development have hindered high-quality development, and the question of how to ensure the optimal development of urban agglomerations has received wide attention worldwide.The trend of development of urban agglomerations has been towards polycentric cities, with the middle reaches of the Yangtze River urban agglomeration comprising three city subgroups with obvious polycentric structure. However, Wuhan metropolitan area has an obvious centric structure; and the growth pole of Poyang Lake urban agglomeration is not prominent, the interactive development of peripheral cities of the Changzhutan urban agglomeration is insufficient, and the internal development of the urban agglomeration is uncoordinated. To promote the coordinated and sustainable development of the middle reaches of Yangtze River urban agglomeration, the gravity of the leading political and economic growth poles of the middle reaches of Yangtze River urban agglomeration was examined while improving the gravity model and geo-coefficient. The potential urban development of each prefecture-level city in the urban agglomeration was measured, the evolution of the spatial structure of the potential growth cities was explored, and the potential growth poles in the region were confirmed by combining the needs of coordinated development of the urban agglomeration. The study aimed to promote the regional economy to the level of high-quality development through optimizing the spatial structure of urban agglomerations, to provide explorative directions for promoting coordinated development of large, medium, and small cities. The study showed that 1) the potential development cities in the middle reaches of the Yangtze River urban agglomeration were unevenly distributed, with Hunan, Hubei, and Jiangxi provinces, respectively, having "high-value equalization", "double-core" and "single-core" network structures. 2) The absolute geopolitical coefficients had clear geographical differentiation. The geopolitical coefficients of cities outside Hubei were mostly smaller than the medians, meaning that the economic gravity was smaller than the political gravity, whereas the three urban subgroups had more internal connections while there were relatively few links between provinces. Hunan and Jiangxi provinces were characterized as "low center and high surroundings". The best geopolitical coefficients were of "bimodal" form and the development level of cities that were under the influence of political gravity was better than for those under the influence of economic gravity. (3) The potential growth cities had characteristics of "marginality" and were concentrated in the southwest and the periphery of urban clusters. In 2017, the overall potential development of Hunan Province was similar to that of its urban centers, tending to be "high-value balanced". It was the province with the greatest potential for cultivating potential growth cities. The "siphoning effect" of Wuhan City was obvious, and the cities with slight potential were the most "marginalized" in the Hubei Province owing to their geopolitical distance. Urban development in Jiangxi Province was more erratic, and its overall potential development was not outstanding. (4) Three primary growth poles in Zhuzhou, Xiangyang, and Jiujiang and three secondary potential growth poles with realistic needs in Hengyang, Yichang, and Xinyu were identified by combining the potential and coordinated development of urban clusters.

Key words: potential growth city, improved gravity model, geopolitical coefficient, the middle Yangtze urban agglomeration