Scaling of the morphology of African cities

Scaling of the morphology of African cities

Edited by Karen Seto, Yale University, New Haven, CT; received August 19, 2022; accepted December 12, 2022

February 23, 2023

120 (9) e2214254120


The emptiness, elongation, and sprawl of a city have lasting implications for cities’ future energy needs. This paper creates a publicly available set of urban form indicators and estimates intercity distances. It uses footprint data of millions of buildings in Africa as well as the boundaries of urban agglomerations, street network data, and terrain metrics to detect different extension patterns in almost six thousand cities. These methods estimate the increasingly longer commutes in urban areas and the energy needed to move millions of people. Designing compact, dense, and better-connected urban forms will help cities be more sustainable and liveable.


A large proportion of Africa’s infrastructure is yet to be built. Where and how these new buildings are constructed matters since today’s decisions will last for decades. The resulting morphology of cities has lasting implications for a city’s energy needs. Estimating and projecting these needs has always been challenging in Africa due to the lack of data. Yet, given the sweeping urbanization expected in Africa over the next three decades, this obstacle must be overcome to guide cities toward a trajectory of sustainability and resilience. Based on the location and surface of nearly 200 million buildings on the continent, we estimate the interbuilding distance of almost six thousand cities. Buildings’ footprint data enable the construction of urban form indicators to compare African cities’ elongation, sprawl, and emptiness. We establish the BASE model, where the mean distance between buildings is a functional relation to the number of Buildings and their average Area, as well as the Sprawl and the Elongation of its spatial arrangement. The mean distance between structures in cities—our proxy for its energy demands related to mobility—grows faster than the square root of its population, resulting from the combined impact of a sublinear growth in the number of buildings and a sublinear increase in building size and sprawl. We estimate that when a city doubles its population, it triples its energy demand from transport.

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Data, Materials, and Software Availability


The research was funded by the Austrian Federal Ministry for Climate Action, Environment, Energy, Mobility, Innovation, and Technology (2021-0.664.668) and the Austrian Federal Ministry of the Interior (2022-0.392.231).

Author contributions

R.P.-C. designed research; R.P.-C., J.E.P., and B.A. performed research; R.P.-C., J.E.P., and B.A. analyzed data; and R.P.-C., J.E.P., and B.A. wrote the paper.

Competing interests

The authors declare no competing interest.

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Information & Authors


Published in

Go to Proceedings of the National Academy of Sciences

Proceedings of the National Academy of Sciences

Vol. 120 | No. 9
February 28, 2023



Data, Materials, and Software Availability

Submission history

Received: August 19, 2022

Accepted: December 12, 2022

Published online: February 23, 2023

Published in issue: February 28, 2023


  1. urban form
  2. sustainability
  3. Africa
  4. energy


The research was funded by the Austrian Federal Ministry for Climate Action, Environment, Energy, Mobility, Innovation, and Technology (2021-0.664.668) and the Austrian Federal Ministry of the Interior (2022-0.392.231).

Author Contributions

R.P.-C. designed research; R.P.-C., J.E.P., and B.A. performed research; R.P.-C., J.E.P., and B.A. analyzed data; and R.P.-C., J.E.P., and B.A. wrote the paper.

Competing Interests

The authors declare no competing interest.


This article is a PNAS Direct Submission.



Complexity Science Hub Vienna, 1080, Austria

EAFIT University, Medellin 050022, Colombia

brilé Anderson

Sahel and West Africa Club Secretariat, Organisation for Economic Co-operation and Development, Paris 75016, France


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