Abstract:

Urban agglomerations are strategic highlands for participating in global competition， important carriers of China's new urbanization， growth poles for high-quality regional development， and also the most prominent areas for spatial expansion. However， due to the underlying influence of the spatial structure of urban agglomerations， there is a certain degree of heterogeneity in their expansion patterns and forms. On the basis of defining the spatial structure of urban agglomerations， this paper systematically studied the patterns and forms of spatial expansion in the Lanzhou-Xining urban agglomeration and the Ningxia Yellow River urban agglomeration using nighttime light data. The results showed that： （1） Both urban agglomerations were mainly characterized by marginal expansion， with enclave expansion as a supplement. From 2011 to 2015， the enclave style expansion of the LXUA was higher than that of the NXUA. From 2016 to 2020， the enclave style expansion of the NXUA was outstanding. Implying that dual core-dual province urban agglomerations prefer to seek new development space in different locations （spatial discontinuity）， while single core urban agglomerations prefer spatial sprawl （spatial continuity）. Filling expansion is generally insufficient， indicating a weak trend of spatial integration in urban agglomerations. （2） The NP and FRAC-AM of the LXUA are higher than those of the NXUA， indicating that the expansion of the dual core dual province urban agglomeration is more obvious and the form is more complex； The COHENSION， AI， and PD indices of the LXUA are lower than those of the NXUA， indicating a higher degree of fragmentation and more prominent spatial dispersion in the dual core dual province urban agglomeration. The NP and PD indices of the two major urban agglomerations are increasing， while the FRAC-AM index decreases， while AI and COHENSION first increase and then decrease， showing a certain degree of convergence. However， the change rate of the dual core dual provincial urban agglomeration is relatively fast， indicating the distribution characteristics of the dual core and cross provincial regions. In fact， it reduces patch density， inhibits patch aggregation， and widens patch separation， which is not conducive to the optimization of the spatial structure of the urban agglomeration.

Key words: spatial structure of urban agglomerations, expansion mode, expansion form, Lanzhou-Xining Urban Agglomeration（LXUA）, Ningxia urban agglomeration along the Yellow River （NXUA）