Research on spatiotemporal patterns and influencing factors of county-level urban shrinkage in urbanizing China

County-level cities, as small-scale urban units in China's urban system, have shrunk due to uneven urban development in urbanizing China. This research constructed a framework for understanding China's county-level urban shrinkage. It defined county-level cities and measured shrinkage using the city shrinkage model, explored the spatiotemporal patterns combined with shrinking degrees and trajectories, and analysed the shrinking types based on city and city periphery perspectives. Then, the influencing factors were identified via the OLS regression model. Taking 2846 county-level cities as research units, the results showed that 180 and 1050 county-level cities shrunk in 2000–2010 and 2010–2020, respectively. Slight and moderate shrinkage dominated, but the proportions of high and severe shrinkage noticeably increased. In terms of shrinking trajectory, recent shrinkage was the main shrinking type. The spatial extent of shrinking county-level cities increased dynamically; the northeast, north, central and northwest regions were core agglomerations, and the east region emerged as an added agglomeration during 2010–2020. Absolute shrinkage became the main shrinking type significantly driven by "city–city" and "off-site urbanization" migration. Urbanization level, economic development, ageing degree, etc., were factors causing shrinkage. This study contributes to advancing understanding among scholars and Chinese policymakers about county-level urban shrinkage in urbanizing China.