The role of subway network in urban spatial structure optimization – Wuhan city as an example

• Urban spatial gravity model and social network analysis are applied to studying Wuhan metro. • Subway increases connectivity by 25%, accessibility by 30.33%, and polycentricity by 7.82%. • Subway construction can significantly improve the accessibility of peripheral districts. The metro transportation network in large cities is one of the most important factors affecting urban spatial structure. To further understand the role of a metro network in the optimization of an urban spatial structure, the panel data of 10 main districts in 2012, 2014, 2016, 2018, and 2020 are selected for the study of Wuhan's metro network. The influence of metro networks on the urban spatial structure is quantified by using urban spatial gravity model and social network analysis. Three indicators - overall network density, centrality, and core–edge are selected to respectively evaluate the connectivity, accessibility, and polycentricity of the spatial structure of the city. The results show that the subway construction increases the spatial connectivity by 25%, the overall accessibility by 30.33%, and the polycentricity by 7.82%. These results demonstrate that the subway construction can significantly improve the connectivity and accessibility of Wuhan’s urban spatial structure, especially the accessibility of peripheral districts, but improving polycentricity is weak. This study reveals the mechanism of action and the degree of influence of the metro network construction process on the dynamic optimization of urban spatial structure in Wuhan at different time stages from the perspective of the overall network. It provides a reference for the study of metro networks in similar cities with topographic and geomorphic diversity and enriches the research cases of such cities.