Urbanisation and why it happens

Urbanisation is an increase in the proportion of a population living in urban areas — not simply more people in cities. That distinction matters: a country whose cities and countryside grow at the same rate is not urbanising.

• Rural–urban migration — the classic driver. Explain it with push factors (mechanisation of agriculture, land fragmentation, rural poverty, drought, conflict) and pull factors (perceived wage differentials, formal-sector jobs, education, healthcare, the "bright lights"). Note the word perceived: expectations often exceed reality, which is exactly why informal settlements grow.
• Natural increase — migrants are disproportionately young adults of reproductive age, so cities have high birth rates and lower death rates than the countryside. In many rapidly growing cities natural increase now contributes more growth than migration does.
• Economic drivers — agglomeration economies: firms cluster to share labour pools, suppliers and knowledge, which raises productivity and pulls in more firms and more workers. This is the self-reinforcing loop behind urban growth.

Examiner's eye: "people move to cities for jobs" is GCSE. A-level says: the rural–urban wage differential, amplified by agglomeration economies, sustains in-migration even when urban unemployment is high — because migrants are responding to expected, not actual, earnings.

Defining the process

Suburbanisation, counter-urbanisation, resurgence

In the developed world the story is not one of endless concentration but of a cycle — outward movement, then a return.

• Suburbanisation — outward spread of the built-up area onto its own edge. Driven by rising real incomes, mass car ownership, arterial roads and rail, cheaper peripheral land, and the desire for space and gardens. Consequences: lower inner-city densities, ribbon development, longer commutes, decline of the inner-city rate base.
• Counter-urbanisation — movement beyond the urban area into rural settlements and small towns, while remaining economically tied to the city. Driven by telecommunications and remote working, retirement, perceived rural idyll, and the ability to sell high and buy low. Consequences: rural house-price inflation, loss of affordable housing for local people, "commuter villages" with weekday emptiness, pressure on the green belt.
• Urban resurgence / re-urbanisation — population and investment returning to the inner city. Driven by de-industrialised land becoming available and cheap, flagship regeneration and cultural quarters, studentification, and a growing group of childless, high-income households who value proximity and amenity.

Careful: the "urban cycle" is a model of the Global North. Many cities in lower-income countries are still in the concentration phase, and some Northern cities show suburbanisation and resurgence simultaneously in different districts. Say so — that is AO2 evaluation, and it earns marks.

Which stage of the urban cycle?

Tap a description, then tap the column it belongs to. Examiners set questions that hinge on telling these three apart.

Size is not the same as power

AQA asks you to separate two ideas that students constantly conflate.

• A megacity is defined purely by size — conventionally a city of more than 10 million people. It is a demographic label. Most new megacities are in Asia and Africa.
• A world (global) city is defined by function. Saskia Sassen's argument is that as production disperses globally, the command-and-control functions needed to coordinate it concentrate in a few cities: corporate headquarters, financial markets, and the advanced producer services (law, accountancy, advertising, management consultancy) that make global business possible. Add cultural and political reach, world-class universities, hub airports and media influence.

So a city can be enormous and not a world city; and a city can be modest in population and be a very powerful world city. Sassen's key move is to treat the world city not as a place with lots of people but as a node in a network — and networks are ranked by connectivity, not headcount.

Evaluative angle: world-city status is double-edged. Command-and-control functions bring capital, but they also polarise the labour market — very high-paid professional work alongside low-paid service work that supports it, with the middle hollowed out. That polarisation is the mechanism behind much of the urban inequality you will discuss later.

Megacity or world city?

Burgess and Hoyt — heuristics, not maps

Two twentieth-century models still frame the way we describe urban land use. Learn what each claims, and then learn why each fails.

• Burgess (concentric zone) — a CBD, a decaying zone of transition, then successively better housing outwards, driven by invasion-and-succession and by the bid-rent logic that land value falls with distance from the centre.
• Hoyt (sector) — land uses grow outwards along transport corridors in wedges: once a high-class sector is established, it extends outward rather than being ringed.
• Limitations: both assume a single dominant CBD; both were derived from industrial-era American cities with car-based commuting; neither anticipates edge cities, out-of-town retail, planning constraints such as the green belt, or the deliberately fragmented, decentred post-modern city. They also ignore culture, ethnicity, planning policy and the state.

The post-modern western city

Where the modernist city was zoned, functional and centred, the post-modern city is fragmented, plural, playful, and organised around consumption rather than production. AQA names the landscapes you should be able to describe:

• Town-centre mixed development — flats above shops above offices; the deliberate reversal of single-use zoning to keep centres alive after 6pm.
• Cultural and heritage quarters — museums, galleries, restored industrial buildings marketed as a "quarter". A tool of place-marketing and inward investment.
• Gentrified areas — individual, incremental renovation by incoming higher-income households. Raises the housing stock and the tax base, but displaces lower-income residents through rising rents and changes the retail mix.
• Fortress developments — gated communities, CCTV, private security, defensive street furniture, "hostile architecture". The privatisation of what was public space.
• Edge cities — self-contained concentrations of office, retail and leisure on the urban periphery, usually at motorway junctions, with more jobs than bedrooms. They break the single-CBD assumption completely.

The critical line: almost all of these landscapes are exclusive as well as attractive. Regeneration and gentrification look identical on a photograph; the difference is who bears the cost. That tension is the natural spine of a 20-mark essay on new urban landscapes.

Naming the landscape

Segregation, inequality, deprivation, diversity

Cities do not distribute advantage evenly, and the pattern is not accidental — it is produced by housing markets, planning and labour markets.

• Economic inequality — a polarised labour market (see world cities) plus a housing market that converts income differences into spatial differences. Deprivation is measured multi-dimensionally: income, employment, health, education, crime, housing, environment.
• Social segregation — clustering by ethnicity, income or age. Explain it through choice (support networks, places of worship, shops, language, safety in numbers) and constraint (discrimination in housing and lending, the price of housing, allocation policies). A good answer refuses to pick one: segregation is nearly always both.
• Cultural diversity — a genuine urban asset: entrepreneurship, cuisine, music, festivals, labour supply. But diversity coexisting with deprivation is not the same as diversity being celebrated.
• Megacities of the Global South — the additional characteristics AQA names: informal settlements (self-built housing, insecure tenure, often on hazardous marginal land), the informal economy (unregistered, untaxed, insecure — but frequently the majority of employment), and infrastructure deficits in water, sanitation and transport.

Nuance that earns marks: informal settlements are sites of enormous ingenuity and enterprise, not merely of misery. Slum-upgrading policies (site-and-service, land titling, incremental self-help) succeed precisely because they build on that capacity rather than bulldozing it.

The urban heat island

The urban heat island (UHI) is the tendency for urban air (and surface) temperatures to exceed those of the surrounding countryside. UHI intensity is simply the urban–rural temperature difference. It is typically strongest on a calm, clear night — because wind mixes the air away and cloud limits both daytime heating and night-time cooling.

Causes — learn all six, and know which dominates at night:

• Surface materials: concrete, brick, asphalt have low albedo (absorb more short-wave radiation) and high thermal capacity — they store heat by day and re-radiate it as long-wave radiation after sunset. This is the dominant night-time cause.
• Anthropogenic heat: waste heat from buildings, industry, vehicles and air-conditioning is a direct energy input the countryside does not have.
• Reduced evapotranspiration: less vegetation and less standing water means less energy goes into latent heat (evaporation) and more into sensible heat — you feel it as temperature.
• Street-canyon geometry: tall buildings on narrow streets trap radiation through multiple reflections and reduce the sky-view factor, so long-wave radiation cannot escape to space at night.
• Pollution dome: particulates and gases absorb and re-emit outgoing long-wave radiation, and reduce night-time radiative cooling.
• Shelter: buildings reduce mean wind speed across the city, cutting the turbulent mixing that would otherwise disperse the warm air.

Your turn — UHI intensity

Why is the UHI a night-time phenomenon?

The rest of the urban atmosphere

• Precipitation and fog. Cities can be wetter than their surroundings: extra thermal uplift from the UHI plus mechanical uplift over rough building surfaces, with abundant condensation nuclei from combustion. Downwind of large cities, convective storm frequency is often enhanced. Urban fog forms readily where nuclei are plentiful — the classic industrial smog of the coal era.
• Wind. Mean wind speed across the city is lower (buildings increase surface roughness), yet gustiness and turbulence are higher. Where air is forced through a narrow gap between tall blocks it accelerates — the Venturi effect — producing dangerous street-level winds; and eddies form on the lee side of towers. Deep in a narrow canyon the air can be almost calm.
• Air pollution. Two families: particulates (PM10, PM2.5, largely combustion and tyre/brake wear) and gases (NOx, SO₂, CO, VOCs). Photochemical smog forms when sunlight acts on NOx and VOCs to generate ground-level ozone — a secondary pollutant, so it peaks downwind and in the afternoon.
• Temperature inversion is the trap: a layer of warmer air aloft sits over cooler surface air, so the polluted air cannot rise and disperse. Basin-shaped or valley cities with anticyclonic weather are especially vulnerable. Note the interaction: the pollution dome then reinforces the UHI.
• Management. Clean-air legislation and smoke-control zones; low-emission and ultra-low-emission zones with charges for older vehicles; congestion charging; investment in public transport, cycling and pedestrianisation; vehicle emission standards and catalytic converters; the shift to electric vehicles. Evaluate: charging zones cut pollutant concentrations inside the zone but raise equity concerns — the poorest drivers own the oldest vehicles — and can displace traffic to the boundary.

Name that urban process

Tap a description on the left, then the term it defines. Precision with these terms is what separates description from explanation.

Why cities flood

Urbanisation transforms the drainage-basin system you met in the water and carbon cycles unit. The mechanism is worth stating precisely, because the marks are in the chain of reasoning:

• Impermeable surfaces (roofs, roads, car parks) remove infiltration and interception almost entirely, and eliminate depression storage.
• Storm drains and culverted rivers are hydraulically smooth and direct — they do deliberately what a natural catchment resists.
• Combined sewers carry foul water and surface run-off together. In heavy rain they exceed capacity and discharge untreated sewage through combined sewer overflows — the pollution problem that follows directly from the drainage design.
• Sustainable drainage systems (SuDS) reverse the chain: permeable paving, green roofs, swales, detention and retention basins, rain gardens, soakaways. They restore infiltration and storage, lengthen lag time, lower peak discharge, filter pollutants, and add amenity and habitat.
• River restoration and de-culverting — re-meandering, removing concrete channels, reconnecting floodplains, replanting banks. Slower flow, more storage, better ecology, higher amenity value; but it needs land, which is the one thing cities are short of.

Your turn — impermeable surfaces and run-off

Waste streams and the waste hierarchy

Waste is the city's largest visible output. Start by separating the streams: domestic/municipal, commercial, industrial, construction and demolition, agricultural, and hazardous/e-waste. The mix reflects the level of development — richer cities produce more packaging and electronics; poorer cities produce a higher organic fraction, which matters because organics are what generate methane in landfill.

Disposal options — and the honest trade-off in each:

• Landfill — cheap and simple, but consumes land, generates methane (a potent greenhouse gas, though it can be captured) and leachate that threatens groundwater. Requires liners and long-term monitoring.
• Incineration / energy recovery — cuts volume dramatically and generates electricity and heat, but requires costly flue-gas treatment (dioxins, particulates), still produces ash needing disposal, and — the key critique — creates a long-run demand for waste that competes with recycling.
• Recycling — conserves materials and energy, but depends on separation quality, market prices for secondary materials, and the energy cost of collection and reprocessing.
• Composting and anaerobic digestion — divert the organic fraction from landfill and return nutrients to soil; digestion also yields biogas.
• Trade in waste — waste is exported, historically to lower-income countries. It is efficient on paper and profoundly unequal in practice, and importing countries have increasingly refused contaminated loads. It also lets exporting cities under-report their true footprint.

Other environmental issues: water contamination (industrial effluent, sewer overflows, urban run-off carrying oil and heavy metals), soil contamination on brownfield sites, and dereliction — which blights land values, invites further neglect and is expensive to remediate. Brownfield redevelopment protects greenfield land, but only if someone pays the clean-up cost.

Evaluating incineration

The liveable city, and the contrasting pair

The ecological (environmental) footprint is the land and water area required to supply a population's resources and absorb its waste. Cities are the classic case of a footprint far larger than the area they occupy: they are parasitic on their hinterlands — which is another way of saying they are open systems with very large inputs and outputs.

• Transport — mass transit, integrated ticketing, cycling infrastructure, pedestrianisation, congestion and low-emission charging, transit-oriented density.
• Energy and buildings — district heating and CHP, retrofit and insulation, building standards, decentralised renewables.
• Green infrastructure — parks, street trees, green roofs and walls, urban wetlands. Note how these multi-task: they cool the UHI, intercept rainfall and slow run-off, filter particulates, sequester carbon and deliver amenity. Multi-functionality is what makes green infrastructure such a strong exam example.
• Waste and water — circular-economy targets, water recycling, SuDS as standard in new development.
• Governance and equity — the sustainable city must also be a just city. Retrofitting only affluent districts, or greening a neighbourhood so successfully that its residents are priced out (green gentrification), fails the social pillar of sustainability while ticking the environmental one.

Case study — the contrasting pair. AQA requires two contrasting cities, showing their urban form, the social and economic issues they face, and their environmental problems and responses. Whichever pair your school uses, structure them identically so the contrast is visible: (1) context and growth trajectory; (2) urban form and how well the classic models fit; (3) social/economic issues; (4) environmental issues — heat, water, air, waste; (5) responses, and an honest evaluation of who benefits. Use figures only where you are certain of them: a precise mechanism earns more than a half-remembered statistic, and an invented statistic is penalised.

Writing the evaluative essay

Paper 2 essays reward AO1 (knowledge), AO2 (application, analysis and evaluation) and, above all, a conclusion that answers the question. For "To what extent…" / "Assess…":

• Unpack the command and the key term. "Sustainable" — environmentally, economically or socially? Say which you will use, and say it in the introduction along with your line of argument.
• Argue in blocks, not lists. Each paragraph = claim + mechanism + evidence + a "but".
• Use the scale lever. Almost every urban judgement changes with scale: a low-emission zone improves air quality within the zone while displacing traffic to its boundary; a city can be locally green while exporting its footprint globally. Making that distinction explicit is a fast route to the top band.
• Use the equity lever. Ask who gains and who pays. Gentrification, regeneration, charging zones and green infrastructure all have distributional effects — naming them is genuine evaluation, not opinion.
• Conclude with judgement, not summary. State to what extent, and the condition on which your judgement depends.

Try it: "Assess the extent to which urban regeneration can solve the social and economic problems of contemporary cities." Plan three blocks — (1) what regeneration demonstrably does: raises the tax base, replaces derelict land, creates jobs and improves the physical environment; (2) what it displaces rather than solves: rising rents push out the very residents whose deprivation justified the scheme, and new jobs may not match existing skills; (3) the conditions under which it does work: affordable-housing quotas, skills and training tied to the scheme, community involvement in design, long-term local ownership. Judgement: regeneration reliably solves the physical problem and only conditionally solves the social one — because the mechanism that funds it (rising land value) is the same mechanism that displaces people.

Sharpening the judgement

The big ideas to know

That is AQA 3.2.3. Press Finish to see your score.