Urban expansion of the 43 worlds’ largest megacities: A search for unified macro-patterns

Abstract

In this article, we make the case for the existence of global macro-patterns of urban change and urban growth, in particular, which may be recognized across metropolitan systems located around the globe. In order to achieve these goals, we examine the pace and types of built-up land expansion inside metropolitan regions of the 43 major megacities in the globe between 1985 and 2015. We show that the advancement of the urbanization-metropolisation process involves the sequential co-occurrence of three urban growth modes (outlying, edge expansion, and infilling). It refutes earlier claims that the three expansion modes occur simultaneously (concurrent co-occurrence) and supports the diffusion-coalescence hypothesis of urbanization. Additionally, we suggest a straightforward model based on the urban scaling laws that can be used to predict the growth of new built-up land in metropolitan areas based on the current urban mass (agglomeration effect), the availability of undeveloped land (hinterland effect), and fundamental structural elements of wider settlement systems (national-level urbanization rate and fertility). We find that the agglomeration effect is crucial for urban infilling while the hinterland effect has a greater impact on edge expansion and outlying growth. We also predict that built-up land inside the administrative regions of the studied megacities will expand by 15% (11,000 sq. km.) between 2015 and 2030. Our research thereby advances knowledge of the physical development of urban systems.