HookIn 2007 humanity crossed a line it can never cross back
Sometime in 2007, according to the United Nations, a threshold was quietly crossed: for the first time in the history of the species, more people lived in towns and cities than in the countryside. There was no single moment you could photograph, but the trend behind it is the defining human geography of our age. In 1950 fewer than a third of people were urban; today it is around 57%, and by 2050 the UN expects roughly two-thirds of a much larger population to be city-dwellers. The scale is staggering — the world now has more than thirty megacities of over ten million people, most of them in Asia and Africa, growing so fast that planning and services cannot keep pace.
That rush into cities is the root of everything in this topic. Concentrating millions of people and their activity into a small area generates a distinctive set of problems the countryside never faces: extremes of wealth and poverty side by side, a self-made local climate hotter and dirtier than the land around it, a drainage system overwhelmed by concrete, and mountains of waste with nowhere to go. The examiner's question is always the same underlying one: as cities swell, how do we manage the social, economic and environmental pressures urbanisation creates — and can the twenty-first-century city be made sustainable before those pressures overwhelm it?
ModelUrbanisation and the urban cycle — how cities grow, empty and refill
Urbanisation is the rising proportion of a population living in urban areas, driven by rural–urban migration (people pulled by jobs and pushed by rural poverty) and by natural increase in young city populations. But AQA wants the whole cycle, not just growth. Suburbanisation is the outward spread of the city as people and businesses move to the edge, aided by the car. Counter-urbanisation is the movement of people out of cities altogether into rural areas, a strong trend in post-war Britain as commuters and retirees sought village life. And urban resurgence (re-urbanisation) is the movement back into city centres, driven by regeneration and the return of young professionals.
Behind these lie deeper economic processes. Deindustrialisation — the collapse of manufacturing from the 1970s — devastated inner cities such as those of the North of England, and decentralisation pulled retail and offices to out-of-town sites. Governments have responded with successive waves of urban regeneration policy: Urban Development Corporations and Enterprise Zones under the 1980s market-led model, the more community-focused City Challenge (1991) and New Deal for Communities (1998), and today's mix of gentrification and flagship redevelopment. Megacities and world cities (London, New York, Tokyo — the command centres of the global economy) sit at the top of this urban hierarchy, wielding influence far beyond their borders.
MechanismUrban forms and the divided city
Urban form is the physical layout and structure of a city, and AQA asks you to recognise new landscapes and the ideas used to explain them. Contemporary Western cities have grown town-centre mixed developments, cultural and heritage quarters (Liverpool's Albert Dock, Manchester's Northern Quarter), gentrified areas, edge cities (self-contained business and retail nodes on the ring road, a term coined by Joel Garreau in 1991), and 'fortress' landscapes of gated communities and defensive design. The post-modern city — theorised by the 'Los Angeles School' of geographers such as Michael Dear and Edward Soja — abandons the neat concentric zones of older models for a fragmented, sprawling, multi-centred landscape where spectacle and private security dominate. Cities in emerging economies show a different form again: a modern high-rise core ringed by vast informal settlements.
Those forms map onto sharp social and economic issues: economic inequality, social segregation (rich and poor sorting into separate districts) and cultural diversity. Segregation arises from differences in wealth, from ethnicity and from planning and housing markets; London ranges from billionaire Kensington to some of the country's most deprived wards in the same city. Cultural diversity brings vibrancy but can bring tension. Managing these divides — through affordable housing, mixed-tenure schemes, anti-discrimination policy and community cohesion programmes — is a core evaluative theme, and the honest answer is that regeneration too often widens the gap it claims to close.
MechanismThe urban climate — a city makes its own weather
A large city measurably alters its local atmosphere. The best-known effect is the urban heat island (UHI): city centres are consistently warmer than the surrounding countryside, and on a still, clear night London can be up to 7–10°C warmer than the rural fringe. The causes are a chain of processes worth stating in order: dark surfaces (tarmac, brick) have a low albedo and absorb solar radiation by day, then release it slowly at night; the urban 'canyon' geometry of tall buildings traps that heat; concrete and stone have a high thermal capacity; there is little vegetation and water to cool the air by evapotranspiration; and human activity — traffic, heating, air-conditioning — pumps out waste heat directly.
Cities also change precipitation (more convectional uplift over the warm, dust-laden air can trigger heavier city thunderstorms), fog and wind. Wind is reshaped by buildings: the tall blocks funnel and accelerate air through the Venturi effect, creating fierce gusts at street level, while sheltered courtyards sit almost still. Most seriously, cities concentrate air pollution — nitrogen dioxide and fine particulates from vehicles, and photochemical smog where sunlight cooks vehicle emissions (notoriously in Los Angeles). The human cost is real: air pollution is linked to thousands of premature deaths a year in London, and in a landmark 2020 ruling nine-year-old Ella Kissi-Debrah became the first person in the UK to have air pollution formally recorded as a cause of death. Cities fight back with policy: London's Ultra Low Emission Zone (launched 2019, expanded London-wide in 2023) charges the most polluting vehicles and has cut roadside nitrogen dioxide.
DataUrban drainage — why concrete makes floods
Replacing fields with roofs and roads transforms a catchment's hydrology. Natural ground is permeable: rain infiltrates, is stored and slowly released, so river levels rise gently. An urban surface is impermeable: rain cannot soak in, so it runs straight off into drains and reaches the river fast. The result is a flashy storm hydrograph — a short lag time, a steep rising limb and a high peak discharge — which is why cities flood suddenly in heavy rain. Drains and culverts, designed to remove water quickly, only sharpen the peak downstream.
The modern management response is Sustainable urban Drainage Systems (SUDS), which aim to mimic natural drainage: permeable paving, green roofs, swales (shallow vegetated channels), infiltration basins and retention ponds that slow, store and clean the water before it reaches the river. The residential SUDS scheme at Lamb Drove in Cambridgeshire, monitored after construction, showed permeable paving and ponds could hold back runoff and cut peak flows close to greenfield rates. River restoration — reopening culverted urban streams and rebuilding natural channels — pushes the same principle further.
Worked runoff calculation. Take a 1 km² (1,000,000 m²) greenfield catchment and a single 40 mm storm. Total rainfall falling on it is 0.040 m × 1,000,000 m² = 40,000 m³ of water. In its natural state the ground is porous, so suppose only about 10% runs off — a runoff coefficient of 0.10. Surface runoff = 40,000 × 0.10 = 4,000 m³, with the other 90% infiltrating and being released slowly. Now pave that catchment for a housing estate so that roofs and roads make it roughly 70% impermeable, lifting the runoff coefficient to about 0.70. Surface runoff = 40,000 × 0.70 = 28,000 m³. The same storm now delivers seven times as much water to the drains, and it arrives far faster — a shorter lag time and a higher peak discharge. That single ratio, 4,000 against 28,000 cubic metres, is the entire justification for SUDS: their target is to hold urban runoff back down toward that original greenfield figure. Quoting the calculation, not just asserting 'concrete causes floods', is what converts an AO1 point into an AO3-credited one.
MechanismWaste, pollution and dereliction — the city's exhaust
A large city is a vast generator of waste, and how it is disposed of is a set-piece comparison. AQA wants you to weigh contrasting approaches. Landfill (burial) is cheap but consumes land and emits methane, a potent greenhouse gas; the UK has steadily driven waste away from it with the Landfill Tax. Incineration with energy recovery — such as London's Edmonton plant — cuts volume and generates electricity but raises concerns about emissions. Recycling and recovery reduce raw-material demand but depend on public participation and stable export markets; for years developed cities exported plastic waste to China until its 2018 import ban forced a rethink. Trade in waste and submergence are further options, each with an environmental cost. The sustainability principle is the waste hierarchy: reduce, reuse, recycle before recover or dispose.
Beyond household waste, cities face other environmental issues the spec flags: atmospheric pollution (covered above), water pollution from industry, sewage overflow and urban runoff carrying oil and heavy metals into rivers, and dereliction — the blighted, contaminated 'brownfield' land left by deindustrialisation. Strategies to manage these include stricter emissions and discharge regulation, clean-up and remediation of contaminated sites, and reusing brownfield land for regeneration rather than building on greenfield. Each strategy trades cost against benefit, which is exactly the evaluation an essay must weigh.
CaseSustainable cities and the two-city case study
Sustainable urban development means meeting the needs of today's city dwellers without compromising future generations — shrinking a city's ecological footprint (the land and resources it consumes) while keeping it liveable. The toolkit is broad: renewable energy and living roofs, water conservation and SUDS, integrated public transport and congestion reduction, compact mixed-use urban form that cuts the need to travel, and genuine recycling. Real exemplars anchor the theory: London's BedZED (the Beddington Zero Energy Development in Sutton, completed 2002) built 99 homes around passive solar design and on-site renewables; the Vauban district of Freiburg in Germany is a near car-free, solar-powered neighbourhood; and Curitiba in Brazil pioneered Bus Rapid Transit from the 1970s, moving millions cheaply and cutting car dependence.
AQA requires case studies of one major city in a developed country and one in a developing or emerging country to illustrate these themes, plus a local-scale study of urban drainage or waste. London serves the developed-world case: deindustrialisation and Docklands regeneration, a pronounced heat island, the ULEZ air-quality fight, congestion charging (2003) and the 2012 Olympic regeneration of the Lower Lea Valley. For the emerging-world case, Mumbai's Dharavi — one of Asia's largest informal settlements, home to perhaps a million people on around two square kilometres — showcases the housing, sanitation, water and waste pressures of rapid urbanisation, alongside a recycling economy and contested redevelopment plans. Two contrasting cities let you apply every theme in the topic to real, named, defensible detail, which is precisely what the extended essays demand.
VocabularyKey terms the mark scheme pays for
TrapsMisconceptions that cost marks
ExamWhat examiners want
Contemporary urban environments is examined against AO1 (knowledge of urban processes at a range of scales), AO2 (application, especially to your case-study cities and to unseen data) and AO3 (interpreting the figures, maps and hydrographs the paper supplies). The short data-response questions are AO3-heavy: read the storm hydrograph or pollution graph precisely, quote specific values, describe the trend and any anomaly, and — where the numbers allow — do the calculation (runoff, percentage change, UHI intensity) rather than describing it in words.
The 20-mark essays reward the same discipline as the rest of Paper 2: AQA's top level wants a balanced, well-evidenced argument reaching a substantiated judgement, so plan management questions as an evaluation of competing strategies (SUDS versus hard engineering, the ULEZ versus its cost to drivers, incineration versus recycling) rather than a description of one. Your two case-study cities are the evidence bank that separates bands — deploy London and Mumbai with named, dated, quantified detail (the ULEZ from 2019, Dharavi's million residents on two square kilometres, BedZED's 99 homes), because precise attribution is the clearest marker of top-band work. Always answer the exact command word: 'assess', 'evaluate' and 'to what extent' each demand a reasoned conclusion, and the mark for judgement is the one weaker candidates leave on the table.