Settlement scaling law reveals population-land tensions in 7000+ African urban agglomerations

Abstract

Allometric urban scaling law quantifies disproportional relationships between urban indicators and city size, which has been reported across developed countries and parts of the global south, but its applicability in Africa is neglected. Here, taking built-up areas derived from remote sensing in more than 7000 African agglomerations in 2015 as examples, we systematically investigate this settlement scaling law from continental, regional, and country levels. Results show that the built-up area linearly scales with population across the African continent and within northern and western Africa, while it sub-linearly scales with population in southern (β = 0.85, 95% CI: 0.808–0.891) and central (β = 0.93, 95% CI: 0.906–0.957) Africa, but super-linearly (β = 1.10, 95% CI:1.068–1.121) in eastern Africa. National settlement scaling exponents (β) vary from 0.65 to 1.25 with an average of 0.96, whose 63.6% variance can be explained by their share of built-up area, share of metropolitan population, GDP per capita, and proportion of slum dwellers. Residuals of scaling fitting reflect local population-land tensions. Western and eastern Africa are relatively rich in buildable land resources, while northern Africa is relatively poor. This study expanded the settlement scaling theory in Africa and multiple indicators are needed to further understand the rapidly evolving African urban systems.