Exploring the coordination between physical space expansion and social space growth of China's urban agglomerations based on hierarchical analysis

Rapid urbanization in China has led to weak internal coordination among demographic, economic, and social urbanization. Urban spatial expansion determines the urban pattern and is an important element of territorial spatial exploitation. Quantifying the coupling coordination relationship between socioeconomic growth and urban spatial expansion is needed. Using remote sensing data and socioeconomic statistics, we used the coupling coordination degree model (CCDM) and an index system to quantify the spatiotemporal trend and coupling coordination relationship between urban spatial expansion (USE) and socioeconomic growth (SEG) for seven urban agglomerations from 2000 to 2015 at urban agglomeration scale and city scale respectively. The results showed that the three world-class urban agglomerations had the largest urban sprawl, along with the highest degrees of coupling coordination at the urban agglomeration scale. However, USE was slower than SEG in national-level urban agglomerations. At city scale, the provincial capitals and municipalities such as Wuhan, Changsha, Nanchang, Zhengzhou and Changchun had higher coupling coordination degrees than the surrounding cities. The study also found that the coupling coordination degree of the Yangtze River Delta and Jing-Jin-Ji urban agglomeration was higher than all the individual cities, indicating that the integration effect should be taken into consideration in urban agglomeration studies and collaborative development among cities was more conducive to the improvement of the overall coupling coordination degree of urban agglomerations. This study quantified the process of USE and SEG at two scales, identified their complicated coupling coordination relationship among the subsystems of urbanization in different periods, and provided specific policy-relevant suggestions, which will be helpful to the regional planning of China's urban agglomerations in future.