Human populations and urban systems: real-world examples
Named cases you can use in an answer, each under the syllabus point it illustrates and linked to the lesson it comes from.
8 Human populations and urban systems
8.1.1Births and immigration are inputs to a human population.
Switzerland natural increase versus population growth
Switzerland's natural increase is only 0.07 % a year (CBR 8.7, CDR 8.0 per 1,000), yet its population grows at about 0.96 % a year because net migration adds around 37,000 people a year.
Demonstrates that immigration can be the dominant input, so natural increase alone does not explain population growth.
Switzerland Human population
8.1.2Deaths and emigration are outputs from a human population.
Crude death rate versus life expectancy, Switzerland and Niger
Switzerland's crude death rate (8.0 per 1,000) is almost the same as Niger's (8.7), yet Swiss life expectancy is 84.4 years compared with 61.4 years in Niger, because Switzerland's older population produces more deaths per 1,000.
Shows the limits of crude death rate as an output measure, because it ignores age structure.
Switzerland Human population
8.1.3Population dynamics can be quantified and analysed by calculating total fertility rate, life expectancy, doubling time and natural increase.
Niger natural increase and fertility
Niger (2024) has a crude birth rate of 41.4 and a crude death rate of 8.7 per 1,000, giving a natural increase of 3.27 % and a doubling time of about 21 years, with a total fertility rate of 5.93 against a replacement level of 2.29.
Shows how natural increase, the rule of 70 and TFR together quantify very rapid growth in a high-fertility country.
8.1.4The global human population has followed a rapid growth curve. Models are used to predict the growth of the future global human population.
StudyUN World Population Prospects projection
The UN World Population Prospects put the world population at 8.2 billion in 2024, with a global TFR of 2.25 (down from 3.31 in 1990). Under the medium scenario the population peaks at about 10.3 billion in the mid-2080s, and the UN gives an 80% chance of a peak this century.
Quantifies the rapid growth curve and shows how the UN's high, medium and low projections differ according to assumptions about future fertility.
8.1.5Population and migration policies can be employed to directly manage growth rates of human populations.
Japan child-rearing policy and falling births
Japan's Children's Future Strategy (December 2023) raised child-rearing spending by 3.6 trillion yen, with child allowances up to 30,000 yen a month for third children and a 500,000 yen birth payment. Yet in 2025 births fell to a record low of 671,236 (TFR 1.14), and deaths exceeded births by 918,253.
Shows a direct pro-natalist policy built on economic levers that has so far failed to reverse falling fertility, which lets students evaluate policy effectiveness.
Thailand voluntary anti-natalist population policy
Thailand's 1970 national population policy was a voluntary anti-natalist programme. It delivered contraception through the Ministry of Public Health and village volunteers, using humour rather than compulsion. TFR fell from about 5.5 in 1970 to below 2.1 by 1990, and today it is around 1.2.
Demonstrates a successful direct anti-natalist policy delivered by persuasion, and the later problem of overshooting into below-replacement fertility.
8.1.6Human population growth can also be managed indirectly through economic, social, health, development and other policies that have an impact on births, deaths or migration.
Bangladesh Female Secondary School Stipend
Bangladesh's 1994 Female Secondary School Stipend paid girls 25–60 taka a month on condition that they kept up attendance and stayed unmarried until 18 or their SSC exams. Eligible rural girls gained about 0.4 years of schooling, married at least 0.4 years later and had their first birth at least 0.3 years later.
Shows an education policy with no population aim that indirectly lowered the birth input by delaying marriage and first birth, with quasi-experimental evidence.
Rwanda community health workers and Mutuelles de Santé
From 1995 Rwanda built a network of about 45,000 community health workers and Mutuelles de Santé health insurance (over 90% enrolment at its peak). Under-five mortality among the poorest fifth of households fell from 229 to 83 per 1,000 live births between 2000 and 2014.
Demonstrates an indirect health policy cutting the death output, while a family planning programme running at the same time makes it hard to tell which policy caused the change.
8.1.7The composition of human populations can be modelled and compared using age–sex pyramids.
Niger and Switzerland age–sex pyramids
Niger's age–sex pyramid has a very wide base and a median age of 16.5 years, while Switzerland's has a narrow base, a bulge in the working ages and a wide top, with a median age of 43.7 years (2024).
Compares contrasting pyramid shapes, using percentage of the total population, to show how birth rates and life expectancy shape population structure.
8.1.8The demographic transition model (DTM) describes the changing levels of births and deaths in a human population through different stages of development over time.
Niger population growth, stage 2 (demographic transition)
Niger is a stage 2 country: its crude birth rate of 41.4 per 1,000 and death rate of 8.7 per 1,000 give a natural increase of 32.7 per 1,000. That doubles the population in about 21 years, and its pyramid has a very wide base.
Shows how a fallen death rate combined with a still-high birth rate opens the wide gap that drives exponential growth in stage 2, and links that gap to a wide-based pyramid.
Switzerland population growth and immigration
Switzerland has a birth rate of 8.7 and a death rate of 8.0 per 1,000, so its natural increase is only 0.07 per cent, which puts it at the boundary of stages 4 and 5. Yet its population is growing at nearly 1 per cent a year through immigration and is now 1.69 times its 1960 size.
Demonstrates both a low-and-close stage 4/5 profile and a key limitation of the DTM: the model leaves out migration, so it cannot explain growth in a country that has little natural increase.
Switzerland The demographic transition model
8.2.1Urban areas contain urban ecosystems.
Geneva tree cover and night-time heat
An RTS analysis of 129 City of Geneva neighbourhoods during the 2026 summer heatwaves found that every 10 percentage points of extra tree cover was linked with nights about 0.8 °C cooler. The Pâquis (5.6% tree cover) reached over +5.6 °C at 4 a.m. and gravel-covered Plainpalais reached +5.4 °C, while Bout-du-Monde was only +1.7 °C.
Shows biotic components (trees) and abiotic components (sealed mineral surfaces, air temperature) interacting within an urban ecosystem to shape its microclimate.
8.2.2An urban area is a built-up area with a high population density, buildings and infrastructure.
StudyUN urban population estimates, global
In 2018 the UN combined national definitions and reported 55% of the world's population as urban. In 2025 its single Degree of Urbanisation method, based on satellite and census data, put 45% of 8.2 billion people in cities (up from 20% in 1950), with the rest in towns or rural areas.
Demonstrates that how 'urban area' is defined, by population threshold, density or services, changes the urban statistics, so any figure must be quoted with its definition.
2018–2025 Urban areas
8.2.3An urban area works as a system.
Lagos resource inputs and Olusosun landfill
Lagos, a city of over 20 million people, depends on inputs of food, fuel and water from outside the city. Its solid waste output goes to landfills such as Olusosun, where in March 2026 trucks queued 5–14 days to unload and unmanaged waste released methane, while wastewater drains into the lagoon and the Atlantic.
Demonstrates a city as an open system with inputs, storages and outputs, and shows how a blocked output flow builds up storages and causes pollution, which reduces urban resilience.
8.2.5Due to rural–urban migration, a greater proportion of the human population now live in urban rather than rural systems, and this proportion is increasing.
Nigeria urbanisation and migration
Nigeria's urban population rose from about 14% in 1960 to 63% in 2024. By 2022 Lagos was about 40 times its 1960 size, with an estimated 5,000 internal migrants arriving each day. Voluntary pull factors (jobs, schools) combine with forced moves such as the roughly 2.4 million flood displacements of 2022 and violence in the North.
Quantifies rapid rural–urban migration, mostly internal, and separates push from pull factors and forced from voluntary moves.
8.2.6Suburbanization is due to the movement of people from dense central urban areas to lower-density peripheral areas.
Pays de Gex urban growth, France
Between 1970 and 1980 the City of Geneva lost 10% of its population (173,618 to 156,505), while the rest of the canton grew by 22%. Across the border, the Pays de Gex grew from 22,157 people in 1968 to 107,091 in 2023, mainly through in-migration. 309 ha of farmland, forest and natural land were built on there between 2011 and 2021, and 44% of its workers commute into Switzerland.
Shows suburbanisation as people move from a dense centre to lower-density edges while still commuting in, and the urban sprawl and land take that follow.
8.2.7The expansion of urban and suburban systems results in changes to the environment.
River Aire straightening and restoration, Geneva
The River Aire, Geneva, was straightened and concreted in the early 1900s. This sped up and concentrated floodwater towards the built-up area downstream, and water quality fell so far that fishing and swimming were banned from the 1980s. Since 2002, more than 4.5 km has been given a natural bed again, which won the Council of Europe Landscape Award in 2019.
Shows how channel modification changes river flows and water quality, and that planning can also reverse the damage.
Urban sprawl and sealed ground, Pays de Gex
In the Pays de Gex, 309 ha of farmland, forest and natural land were built on between 2011 and 2021 as suburbs spread out from Geneva. About two-thirds of the City of Geneva is now sealed ground, and the peak flows of its small urban streams are tending to rise.
Quantifies how suburban expansion causes loss of farmland and natural land, and how sealed ground raises peak river flows.
8.2.8Urban planning helps decide on the best way to use land and buildings.
Praille-Acacias-Vernets redevelopment, Geneva
Praille-Acacias-Vernets (PAV) in Geneva is a 230 ha industrial zone that the canton voted in 2011 to redevelop. The plan includes about 12,000 homes, 6,000 jobs, a 6–8 ha park, 3,000 trees, 20 km of cycle paths and the reopening of 450 m of the culverted River Drize, but existing firms must be moved elsewhere first.
Demonstrates planners balancing domestic, environmental, physical, industrial and financial stakeholder needs on a single site.
8.2.9Modern urban planning may involve considering the sustainability of the urban system.
Dubai wastewater recycling for irrigation
Dubai recycles about 90% of its wastewater (target 100% by 2030). About 265 million m³ a year irrigates around 10,400 ha of green space, saving about AED 2 billion a year compared with using energy-intensive desalinated water from Jebel Ali.
Shows water reuse as a sustainability measure in urban planning, and raises the question of whether desert greening is truly sustainable.
Dubai, United Arab Emirates Urban planning
8.2.10Ecological urban planning is a more holistic approach that treats the urban system as an ecosystem, understanding the complex relationships between its biotic and abiotic components.
Basel green roof building law
Since 2002, Basel's building law has required green roofs on new and renovated flat roofs, with at least 12 cm of native-planted substrate since 2015. This gives about 5.7 m² of green roof per inhabitant, the most of any city. The roofs cool the rooms below by up to 5 °C and cut runoff by 17–20%, and Brenneisen recorded 79 beetle and 40 spider species, some endangered, on the Rhypark roof.
Demonstrates ecological planning that links abiotic factors (soil depth, runoff, temperature) to biotic communities.
8.3.2Sources of primary pollutants are both natural and anthropogenic.
Saharan dust particulates, Geneva and West Africa
Saharan dust is a natural source of particulates at two ends of its range: about 15 dust days were detected over Geneva in 2025, with a strong episode on 12–15 November, and from December to February the harmattan wind carries dust over Lagos and other West African coastal cities.
Counter-example to the idea that all air pollution is caused by people, showing that natural primary pollutants raise PM levels even where traffic rules are strict.
8.3.3Most common air pollutants in the urban environment are either derived directly or indirectly from combustion of fossil fuels.
Air pollution deaths and costs, Lagos
Lagos, Nigeria: a 2020 World Bank study found air pollution caused about 11,200 early deaths in 2018 (60% children under five), costing US$2.1 billion (2.1% of Lagos State GDP), with mean PM2.5 of 68 µg/m³. Road transport (32%), biomass burning (19%), waste burning (9%) and bush burning (5%) are the main sources, and about half of household energy comes from petrol and diesel generators.
Shows how most urban pollution comes from combustion, with fossil-fuel traffic and generators as the largest share, and puts a number on the health and economic cost.
8.3.4A range of different management and intervention strategies can be used to reduce urban air pollution.
Léman Express and Lagos Blue Line ridership
The Léman Express cross-border rail network opened in December 2019 with 45 stations and carried over 80,000 passengers a day by 2024. By contrast, the 13 km Lagos Blue Line, opened in September 2023, carried only about 15,000 a day in 2025.
Compares improved public transport in two cities and shows that one new rail line cannot do much where biomass, waste and generator burning are major sources.
Stick'AIR emergency traffic plan, Geneva
Geneva's Stick'AIR emergency traffic plan, switched on in August 2025 for only the second time since 2020, kept out vehicles without the right sticker. These were about 11% of the canton's vehicles but produced 30% of vehicle NOx, and public transport can be made free on high-pollution days.
Demonstrates a limited-car-use strategy aimed at the highest emitters, so a small cut in vehicle numbers gives a much bigger cut in NOx.
8.3.5NOx and sulfur dioxide react with water and oxygen in the air to produce nitric and sulfuric acid, resulting in acid rain.
Acid rain from Italy, Ticino (Po Plain source)
Ticino, Switzerland: humid Mediterranean air picks up SO2 and NOx over the industrial Po Plain (Milan, Turin), then rises over the Alps and drops its rain, so much of the acid falling on Ticino comes from Italy, with 70–79% arriving as wet deposition.
Shows that acids form from emitted gases in the atmosphere and fall as wet deposition far from the source, crossing national borders as transboundary pollution.
Ticino, Switzerland Acid deposition
8.3.6Acid rain has impacts on ecology, humans and buildings.
Acidified mountain lakes, Ticino
Ticino's mountain lakes lie on base-poor rock with little buffering capacity. In 1995, 29% of 45 surveyed lakes had a pH below 6.0, compared with 10% of 52 acid-sensitive Swiss lakes in a 2018 study.
Shows that how much damage acid deposition does to freshwater depends on the underlying geology, and that ecosystems can recover once deposition falls.
St Paul's Cathedral balustrade erosion, London
St Paul's Cathedral, London: over 30 years, the limestone balustrade's erosion rate fell from 0.049 to 0.035 mm per year as London's daily SO2 fell from about 80 ppb (early 1980s) to under 3 ppb (late 2000s).
Quantifies how acid deposition dissolves calcium carbonate building stone, and shows that damage slowed towards natural weathering rates once SO2 fell.
8.3.7Management and intervention strategies are used to reduce the impact of sulfur dioxide and NOx on ecosystems and to minimize their effects.
India coal plant scrubber rule relaxation
India's coal power stations emit over 6 million tonnes of SO2 a year. A 2015 rule required scrubbers, but only 57 of 600 units had them by August 2025. In July 2025 the rule was relaxed so that 77% of units were exempt. Rajpura (no scrubbers) emitted about 43,500 t of SO2 in 2025, roughly 11 times more than the similar Mahatma Gandhi plant, which has scrubbers.
Lets students evaluate control at the point of release (flue-gas desulfurisation) by weighing its proven effectiveness against cost, water use, limestone use and extra CO2.
Sulfur and nitrogen deposition decline, Ticino
Thanks to emission cuts across Europe, sulfur deposition in Ticino fell 81% (114 to 22 meq/m²/yr) between 1983–87 and 2018–22. Nitrogen deposition fell only 28% (158 to 114), and more than half of it now comes from farm ammonia.
Shows that international emission reductions worked for sulfur but less well for nitrogen, which comes from many diffuse sources, so further management strategies are needed.