Last lesson you put Niger, Switzerland, Japan and Thailand on one line, the demographic transition model, and argued about where each one sits on it. The model told you how fast each population is growing. It said nothing about where those people live.
That is the question for this lesson. In 1960 only about one person in seven in Nigeria lived in a town or city. Today it is closer to two in three, and Lagos, on the coast, is one of the largest cities in Africa. Closer to home, the City of Geneva lost people in the 1970s while the villages around it grew, and the Pays de Gex, just over the border, has almost quintupled since 1968. People are on the move, and they are not all moving in the same direction.
By the end of the lesson you should be able to say what makes a place urban, treat a city as both an ecosystem and a system, and explain why people move into cities, out to their edges, and sometimes away from them altogether.
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8.2.2 An urban area is a built-up area with a high population density, buildings and infrastructure.
Urban areas have a dense assemblage of buildings and people located close together for residential, cultural, productive, trade and social purposes; rural areas have relatively low population density and dispersed settlements. Cities, towns and suburbs are classified as urban areas.
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8.2.4 Urbanization is the population shift from rural to urban areas.
Urbanization involves the process of land use becoming more built-up, industrialized and dominated by dense and continuous human settlement and infrastructures.
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An urban area is defined by three things together: a high population density, a dense cover of buildings, and the infrastructure that serves them, such as roads, pipes, power lines and public transport. Notice what the definition includes. It is not only big cities: towns and suburbs count as urban too. A rural area has a low population density and settlements that are spread out.
Urbanisation is not the same as a city getting bigger. It is the shift in the proportion of a population living in urban rather than rural areas. A country's cities can grow simply because their residents have children, and if the countryside grows just as fast, the country has not urbanised at all.
Every country draws the line in its own place. Some count any settlement above a set number of people as urban, and the number varies from country to country; others use density or the services a place has. This matters more than it sounds. In 2018 the United Nations, adding up national definitions, reported that 55% of the world's population lived in urban areas [Source]. In 2025 it switched to a single method applied to every country from satellite and census data, the Degree of Urbanisation, which sorts places into cities, towns and rural areas. On that method, 45% of the world's 8.2 billion people live in cities, against 20% in 1950 [Source]. The rest live in towns or rural areas. The world did not change between the two reports. The ruler did.
The chart below uses national definitions, which is why each country can be compared with itself over time more safely than with another country.
Task 1.1
World Bank, Urban population (% of total population), from UN World Urbanization Prospects (national definitions).
| Urban population (% of total) | 1960 | 1990 | 2024 |
|---|---|---|---|
| Niger | 5.7 | 15.4 | 18.0 |
| Thailand | 11.8 | 18.8 | 61.9 |
| Nigeria | 14.2 | 35.2 | 63.0 |
| Switzerland | 51.0 | 68.7 | 85.5 |
| Japan | 63.3 | 77.3 | 92.2 |
World Bank, Urban population (% of total population), from UN World Urbanization Prospects, national definitions [Source]
Task 1.2
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8.2.1 Urban areas contain urban ecosystems.
Urban ecosystems, like all ecosystems, are composed of biotic components (plants, animals and other forms of life) and abiotic components (soil, water, air, climate and topography).
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Image from the RTS analysis of Geneva's hot summer nights
Image from the RTS analysis of Geneva's hot summer nights
Image: RTS [Source]
A city is an urban ecosystem: people, street trees, parks, birds and insects (the biotic components) living with soil, water, air, climate and topography (the abiotic components). In a city, many of the abiotic surfaces are made by people: asphalt, concrete, gravel and roofs.
In August 2026 the Swiss broadcaster RTS combined seven public data sets to compare 129 neighbourhoods of the City of Geneva during the heatwaves of June and July. It measured how much warmer each neighbourhood was than a covered lawn at 4 a.m., the coolest hour of the night [Source].
Tree cover ranges from 0.8% to 44.6% across the city. On average, every 10 percentage points of extra tree cover was linked with nights 0.8 °C cooler. The analysis found that tall buildings were not the problem: what heated a neighbourhood was the area of sealed, mineral ground. Concrete, asphalt and gravel absorb heat during the day and release it through the night. Trees shade those surfaces, and their leaves give off water vapour, which cools the air.
The authors are careful about one thing: the link between trees and cool nights is a correlation. Wind, distance from the lake and the colour of building materials also play a part.
Task 2.1
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8.2.3 An urban area works as a system.
An urban system is the interconnected system of buildings, microclimate, transport, goods and services, power/energy, water/sewage supply, humans, plants and animals. In urban systems, consider waste/pollution, urban efficiency, sustainability and resilience.
Application of skills: Create a systems flow diagram representing an urban system.
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