Colourful drawing of high-rise buildings. A green vine with hearts for flowers rises up between them.
Image by Prawny on Pixabay

Population Density

Today I want to share with you some of the background reading I did to understand population density: how tightly packed people are on the planet’s surface.

I think density is a key element in designing better future cities. There is a balance to be struck: On the one hand, it is easier to provide services when people live close together and, if we can get people to live in a way that takes up less space, humans will have less impact on the planet. On the other hand, crowded conditions can lead to health problems and be unpleasant to live in. I have been investigating how to measure density, in sensible and easy ways. That turns out to be quite difficult.

The most common way is to count the number of people in a square kilometre (or mile if you are that way inclined). We often use this measure at the national level, where it is easy to divide the total population by the total land area. So, for example, in Singapore there are 8250 people to each square kilometre, in Portugal there are 111 people in the same space and in Namibia, only three! (You can see the full list on Wikipedia.) 

But that is not a very useful measure. People sprawl unevenly across the land, and it gives little information about living conditions. For example, in a city where parts of the land are for public or business use, the population density can look sparse, but the areas that people actually live in can be quite small. Gauteng is the smallest province of South Africa, but it is home to about a third of the population. The average population density is 737 people per square kilometre but the in some parts of the province (Hillbrow and Berea, for those who know Jozi) that number goes up to 63211, close to some of the densest places in the world. To make sense of these numbers, you have to look carefully at each square kilometre.

Another way to understand density is to look at the number of rooms in a dwelling (excluding kitchens and bathrooms) and compare that to the number of people who live there. That tells us if people share rooms most of the time or if they have a room to themselves. This measure was of interest during Covid because it reflected the likelihood that people would be able to self-isolate. Researchers found that, in Gauteng, more than half of the population does have a room of their own, although in the worst cases there can be 3 to 16 people sharing one room. This measure gives a bit more information, but does not account for how big the rooms are. 

Of course, people might reside comfortably in high-density areas if they live in high-rise buildings that are well planned and managed. The external footprint of a building does not reflect the area of the floor space inside. The floor area of each apartment is a better measure, but it would be difficult to collect that data for each dwelling.

This is where technology helps. It is possible to derive the volume of buildings from satellite imagery and radar remote sensing and compared this with estimates of the number of residents. Using this measure for Gauteng, there are sizeable areas where each person has less than 10 cubic meters of living space and similarly extensive areas with between 10 and 50 cubic meters each. Scattered between these are a few areas where the volume per person is 50 to 200 cubic meters and a smattering of luxury suburbs, where each person has between 200 and 1000 cubic meters of space. (You can see the map here.) 

All of this led me to focus on volume in my 2500 world, where I’ve tried to design a hyper-dense city. In that city, I provide just 25 cubic meters of living space for each person. This may sound small, but I also move much of life out of private spaces and into public areas. Private spaces in the ultra high-density city of New Jozi are really just for sleeping. I am not sure that living in such close quarters would be pleasant, but I think it’s an interesting thought experiment to consider how little space we could live in. I'll be publishing Broody in a few weeks, if you want to read about life in the hyper-dense city. 

The excellent people of the Gauteng City Regional Observatory (GCRO) produce fabulous visualisations and lucid explanations of the Gauteng data on their site at