Global increases in built-up volume indicate more divergent and less dispersed urban expansion patterns.

Abstract

Viewing urban spatial structure from a three-dimensional (3D) perspective provides important insights for environmental sustainability. While existing studies mainly examine 3D built-up volume, the spatial distribution of vertical growth remains insufficiently understood. This study investigates centrality and intensity of vertical expansion in newly urbanized areas. Using multi-source remote sensing data, we develop a Centrality Index (CI) and an Intensity Index (II) to characterize 3D urban expansion and compare it with conventional two-dimensional (2D) measures. Results show that: (1) 3D expansion is generally more centralized than 2D expansion. (2) Vertical growth is stronger in the Global South; however, Global South cities outside China, especially in Africa, often demonstrate low 3D centrality. (3) 3D expansion patterns are closely associated with natural and socioeconomic conditions and display strong path dependency. As urbanization shifts toward Africa and South Asia, prevalent low-centrality patterns may improve land-use efficiency but increase commuting-related carbon emissions.