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What does urbanisation mean?

We can conceptualise urbanisation as two expansion processes: one of the cities and the built environment, and one of their populations
Photograph of a public art installation in Dublin, Ireland, with signs pointing out the direction and distance to urban agglomerations of different sizes around the world.
© William Murphy via flickr

We can conceptualise urbanisation as two expansion processes: one of the cities and the built environment, and one of their populations.

Both processes can be expressed in terms of average growth or in terms of their absolute and relative size at any given point in time. Beware that urban growth does not always come at the expense of rural populations, and that whilst urban centres usually sprawl outwards, they can also become more densely populated within their borders.

Megacities or large urban areas may be the first examples that come to mind when thinking about urbanisation. In 1950, we could hardly classify three widely familiar metropolitan areas as being, in fact, metropolitan: London, New York and Tokyo. Currently, there are over 30 of these areas and we can expect another one to be added every couple of years (UN DESA, 2018).

Where urban dwellers live

It is important to be aware, however, that the vast majority of urban dwellers live in thousands of smaller urban agglomerations:

  • More than 48 of these smaller urban areas currently house on average between 5 and 10 million inhabitants
  • 467 smaller urban areas house on average from 1 to 5 million people
  • 598 of these smaller areas house on average between 0.5 and 1 million people (UN DESA, 2018)

While these processes of territorial and demographic urbanisation often go hand in hand, they can move at different rates. Globally, urban land is actually expanding at a higher speed than urban populations. (Seto et al. 2011; Mahtta et al, 2019).

Any of the above numbers, however, rely heavily on one key question: what counts as ‘urban’ in the first place? This blog post raises the question of whether you agree with adopting universal characteristics and parameters, and where you would draw city boundaries and place their population thresholds at a global level.

Harmonised methodology

In March 2020, the United Nations Statistical Commission endorsed a harmonised methodology coined the ‘Degree of Urbanization.’ The United Nations quickly emphasised, however, that this methodology is not meant to replace but only complement nationally determined definition (UN Statistical Commission, 2020: 22). If you are interested in learning more about this, we recommend this additional blogpost.

For the time being, it is safe to conclude that different concepts of the city and urbanisation will remain in parallel use. These can rely on the surface area and population size of concentrated human settlements, as well as include functional and relational criteria.


Mahtta, Richa et al, Building up or spreading out? Typologies of urban growth across 478 cities of 1 million+ (2019): Environmental Research Letters 14 (12) 124077

Seto, Karen et al., A Meta-Analysis of Global Urban Land Expansion (2011): PLoS ONE 6 (8) e23777

UN DESA – Department of Economic and Social Affairs, World Urbanization Prospects (2018)

UN Statistical Commission, Report on the fifty-first session (2020)

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