Urban agglomerations (UAs) have become the urbanized “growth poles”, especially against the background of increasing population flow to cities. The spatial structure of UAs has been deemed the essential factor affecting regional function and sustainable development. Although there have been many meaningful studies on spatial structure changes in China, a systematically comparative work of UAs is still absent. Under this context, this paper examines the changing process of spatial structure in 20 Chinese UAs from monocentric to polycentric during the years 1992–2012 by using the night-time light data—an alternative to census data—and explores the major driving forces underlying the evolution. Our empirical results suggest that there is an obvious polycentric tendency of UAs, the spatial distribution pattern of which is not apparent. Panel regression models reveal that the economic level, the population size, the foreign direct investment (FDI), the human capital, and the transport infrastructure play significant positive roles in shaping the polycentric changing process, while the growth of the government expenditure does the opposite. Moreover, transport infrastructure and FDI are positively associated with polycentric spatial structure in mature UAs; on the contrary, they are negatively associated with it in the emerging UAs. Our study results have important policy implications for rapid Chinese urbanization—the policy whereby “China’s future urbanization development model is to limit the agglomeration of large cities while focusing on developing small and medium-sized cities” may be more efficient in mature UAs.

The urban agglomerations in the Yellow River Basin are important carriers for China’s high-quality development. It is an inevitable trend to promote sustainable development and people’s well-being in the urban agglomerations of the Yellow River Basin. A case study of 70 cities of seven urban agglomerations in the Yellow River Basin from 2011 to 2017 is presented. The two-stage super-efficiency network slacks-based measure (Super-NSBM) model considering undesirable outputs is adopted to measure the ecological well-being performance (EWP), and the spatial correlation analysis method is used to analyze the spatio-temporal evolution characteristics of the EWP. The results show that the average EWP of the seven urban agglomerations in the Yellow River Basin was less than 1, showing a trend of firstly rising and then slowly decreasing. The average EWP presents the distribution pattern of the highest in the middle reaches, followed by the upper reaches, and the lowest in the lower reaches of the Yellow River Basin, respectively. The average ecological economic efficiency in the first stage of urban agglomerations of the Yellow River Basin was greater than the average economic well-being efficiency in the second stage. The average EWP in the Yellow River Basin shows local spatial heterogeneity during the study period. Policy measures are proposed to promote the improvement of the EWP of urban agglomerations in the Yellow River Basin. This study can provide reference for the policy formulation of high-quality green development and sustainable construction of urban agglomeration in the Yellow River Basin.