How the spatial functional division of labor in urban clusters affects urban population size? Evidence from 19 urban clusters in China

Relying on datasets covering 19 urban clusters in China, this study delves into the impact of the spatial functional division of labor in urban clusters (SFDL) on urban population size and its underlying mechanisms. In contrast to the prevailing focus of previous studies on individual city advantages to understand urban population size differences, this paper represents the first large-scale and cross-urban cluster empirical test, extending the research to consider SFDL. The results reveal a positive correlation between SFDL and urban population size. Mechanism analyses demonstrate that SFDL contributes to enlarging urban population size by increasing productivity. Heterogeneity analysis indicates that the positive effect of SFDL is more pronounced in central cities and large to medium-sized cities compared to peripheral and small cities, revealing a trend of population distribution centralization in urban clusters as SFDL deepens. Further discussion reaffirms the trend of population distribution centralization as SFDL deepens. Additionally, urban clusters with State Council-approved development plans exhibit a more significant positive impact of SFDL on urban population size than other urban clusters. These findings provide novel insights into optimizing population distribution from the perspective of urban clusters and offer policy guidance for design in urban cluster development planning.