From dominant edge expansion to increasing infilling: the driving forces behind built-up area fragmentation in Chinese cities

While the patterns of urban expansion are often described, a national-scale understanding of how specific expansion processes mechanistically drive changes in urban landscape pattern is notably lacking. Our study conducted a comprehensive analysis of 366 cities across China from 1995 to 2018. We found a clear temporal shift in China’s urban expansion, characterized by dominant edge expansion, a significant increase in infilling, and a decline in leapfrog, robustly supporting the diffusion-coalescence theory at a national scale. Rapid built-up area growth (287.6%) led to widespread landscape fragmentation, evidenced by increased patch density and decreased compactness. Path analysis revealed that infilling expansion could directly reduce landscape fragmentation, while leapfrog expansion and road density exacerbated it. This study highlighted that optimizing the type, not just the scale, of urban expansion is crucial for sustainable spatial planning, offering policymakers practical insights to mitigate landscape fragmentation.