Towards a more compact urban form: A spatial-temporal study on the multi-dimensional compactness index of urban form in China

Compact urban forms are essential for sustainable development, while few studies developed multidimensional urban form compactness index at the national scale from the perspective of spatial-temporal data, limiting our understanding of urban compactness mechanisms. In this study, a multidimensional urban form compactness index was created for 296 cities in China, focusing on spatial topology, morphology, and dynamics, addressing a gap in national-scale analyses from spatial-temporal viewpoints. Key findings include: (i) In the last two decades, significant alterations have occurred in urban compactness, with cities witnessing enhancements from 2005 to 2020. There's a spatial evolution trend characterized by higher compactness in the southeast and lower in the northwest, advancing from northwest to southeast. (ii) Urban expansion elements generally undermine urban compactness, whereas agglomeration efficiency elements contribute positively. (iii) Over time, while urban expansion impacts have shown relative stability over the years, agglomeration efficiency indicators have undergone an N-shaped fluctuation. Spatially, factors associated with urban sprawl enhance compactness in western and northeastern China, while land use factors are particularly effective in the northeastern, western, and northern areas. The study emphasizes the importance of using multidimensional composite indicators for thorough understanding of urban form compactness, offering significant insights for future policy and urban management.