Applying the Degree of Urbanisation to the globe: A new harmonised definition reveals a different picture of global urbanisation

TLDR

The Degree of Urbanisation, a UN‑endorsed definition of cities, towns, semi‑dense and rural areas, shows urban population shares similar to national definitions in the Americas, Europe and Oceania but considerably higher in Africa and Asia. The study tests whether the Degree of Urbanisation‑defined cities and towns follow Zipf’s law and whether urban population shares correlate positively with economic development. The authors assess the sensitivity of population and land classification by varying population size and density thresholds and by applying a different global population grid. Empirical analysis indicates that towns are classified as rural in Africa and Asia but urban elsewhere, that cities occupy a small but doubling land share over forty years, and that population growth outpaces land expansion, raising densities.

Abstract

The Degree of Urbanisation is a new definition of cities, towns and semi-dense areas, and rural areas endorsed by the UN Statistical Commission. The urban population share according to the Degree of Urbanisation is similar to the one based on national definitions in the Americas, Europe and Oceania, but considerably higher in Africa and Asia. An empirical analysis and a comparison of concepts suggest that towns are likely to be classified as rural areas in Africa and Asia and as urban areas in other parts of the world. The paper shows that cities cover only a small share of land, but this share doubled over the past forty years, as has the number of cities. Although cities have expanded rapidly, their population grew even faster leading to higher densities. The paper tests two classic urban facts: 1) the cities and towns as defined by the Degree of Urbanisation closely follow Zipf's law 2) the population shares in urban areas, cities and especially metropolitan areas are positively and significantly correlated with the level of economic development. Lastly, the sensitivity of the classification of population and land are tested by varying the population size and density thresholds as well using a different global population grid.