Urban structural divergence under pandemic shock: population redistribution and center reconfiguration across Chinese cities

Urban structural change is commonly assessed using measures that rely on the identification of city centers. However, under significant shocks, population distribution and center configurations may evolve simultaneously, rendering direct comparisons of structural indicators potentially incomplete. To address this issue, this study applies a counterfactual decomposition framework that separates population redistribution from center reconfiguration, allowing structural adjustments in large and small cities to be interpreted in terms of distinct underlying mechanisms rather than uniform responses to shock. Using high-resolution LandScan population density data for 319 Chinese cities from 2016 to 2023, we show that city centers generally expanded spatially while becoming less dense, alongside a more even population distribution. Beyond this shared trend, dispersion and polycentricity diverged systematically across city types: subcenters in larger, more developed cities tended to contract or disappear, whereas those in smaller or less developed cities expanded and absorbed population. These findings indicate that post-shock urban structural change is driven not only by redistribution within existing centers but also by heterogeneous reconfigurations of urban centers themselves, underscoring the explanatory value of the proposed decomposition approach.