World cities: categories and causes

Urban Growth and the Hierarchy of Urban Areas

1. Introduction

Urban growth – the increase in size, population and economic activity of cities – is a core theme of Cambridge IGCSE/A‑Level Geography (Paper 2 – Topic 6). It links the key concepts of scale, place, spatial variation and systems. The notes below follow the syllabus structure, give the required depth for AO1–AO3 and provide the case‑study material needed for AO2.

2. Urban Growth

2.1 What is urban growth?

• Population growth – increase in the number of people living in a city.
• Spatial (area) growth – outward or upward expansion of the built environment.
• Both processes interact: more people need more space, and new space can attract more people.

2.2 Processes of population growth

• Natural increase: births – deaths. The exponential model used in the syllabus:
   P_t = P₀ e^rt, where r = annual growth rate.
• Migration:
  • Rural‑to‑urban (most common in LICs & MICs)
  • Inter‑urban (movement between towns/cities within a country)
  • International (often to HICs or major global cities)

2.3 Processes of spatial growth

• Urbanisation – rise in the proportion of a country’s population living in towns and cities.
• Suburbanisation – outward spread of residential and commercial development beyond the historic core.
• Urban sprawl – low‑density, car‑dependent expansion that consumes peri‑urban land.
• Counter‑urbanisation (de‑urbanisation) – movement from cities to smaller towns or rural areas, often linked to telecommuting or lifestyle choice.
• Re‑urbanisation / urban renewal – regeneration of inner‑city areas through redevelopment, gentrification or brownfield conversion.

2.4 Causes of urban growth (multiscale drivers)

2.5 Quantitative illustration of urban‑population growth

Urban‑population growth rates (annual %) for 2022‑2023 (UN‑DESA, World Bank). Two contrasting countries are shown for each income group, as required by the syllabus.

2.6 Consequences of urban growth

• Environmental: loss of agricultural land, increased surface‑runoff, air‑quality deterioration, urban heat‑island effect.
• Social: housing shortages, informal settlements, segregation (income & ethnic), pressure on health & education services.
• Economic: creation of jobs and markets, but also informal‑sector expansion and spatial inequality.
• Political: governance challenges (service delivery, planning), potential for social unrest.
• Rural impacts: labour drain, remittance flows, decline of traditional agriculture, but also “push‑pull” effects that can stimulate rural diversification.

3. Urban Hierarchy and City Categories

3.1 City categories (Cambridge terminology)

3.2 Hierarchy of urban areas (size & function)

3.3 Primate cities

A primate city is at least twice as large as the next biggest city in the country and dominates the national urban system (e.g., Bangkok, Mexico City, Lagos). Primate cities often create policy challenges such as regional imbalance, over‑concentration of services and heightened vulnerability to shocks.

4. Urban Structure and Change

4.1 Horizontal vs. vertical development

• Horizontal (sprawl) – outward, low‑density growth; typical of car‑dependent cities (e.g., many US suburbs).
• Vertical (densification) – growth upwards through high‑rise apartments, mixed‑use towers and brownfield redevelopment; typical of land‑constrained, high‑income cities (e.g., Hong Kong, Manhattan).

4.2 Land‑use zones

1. Central Business District (CBD)
   • Core of specialised commercial activity.
   • High land values, steep land‑value gradient.
   • Transport interchange (major rail, bus, airport links).
   • Functions: finance, headquarters, high‑value retail, professional services.
2. Inner city – older residential stock, often undergoing regeneration or experiencing deprivation.
3. Suburban zone – low‑rise housing, shopping malls, light industry; increasingly mixed‑use.
4. Industrial fringe – factories, logistics parks, usually near major transport routes.
5. Green belt / peri‑urban fringe – agricultural or open land that can be pressured by sprawl.

4.3 Changing location of activities

• De‑industrialisation – loss of manufacturing from inner cities, relocation to peripheral zones or abroad. Case study: Detroit (USA) – decline of auto plants led to population loss and land‑use change.
• Service‑sector relocation – finance, knowledge‑based services moving to specialised districts or edge cities. Case study: Bangalore (India) – IT parks shifted high‑skill jobs from the CBD to the periphery.
• Gentrification – middle‑income groups moving into former low‑income inner‑city areas, raising property values and displacing original residents. Case study: Shoreditch (London) – creative‑industry influx transformed a former industrial district.
• Edge‑city development – new, self‑contained commercial/office nodes outside traditional CBDs. Case study: Gurgaon (India) – rapid emergence of a satellite business hub.

4.4 Residential zonation

• Income‑based zones: high‑income estates (often close to the CBD or in exclusive suburbs), middle‑income suburbs, low‑income peripheral areas or informal settlements.
• Ethnic / cultural zones: historic enclaves such as Chinatowns or Little Indias that persist despite overall city growth.
• Planned zoning: local‑authority policies allocating land for housing, industry, recreation and conservation.

5. Sustainable Urban Development

5.1 Key urban sustainability issues

• Housing shortage & unaffordable rents.
• Transport congestion & air‑quality deterioration.
• Urban heat‑island effect & flood risk from impermeable surfaces.
• Resource consumption (water, energy) and waste generation.
• Social exclusion & spatial inequality.

5.2 Common mitigation & adaptation strategies

1. Compact city policies – higher densities, mixed‑use development, strong public‑transport corridors.
2. Green infrastructure – parks, green roofs, urban forests to reduce heat islands and manage storm‑water.
3. Renewable energy & smart‑grid systems – rooftop solar, district heating, energy‑efficient buildings.
4. Inclusive housing schemes – affordable‑housing quotas, rent‑control, upgrading of informal settlements.
5. Transport reforms – low‑emission zones, cycling networks, integrated ticketing, promotion of public‑transport.

5.3 Evaluation framework (exam‑style)

• Effectiveness – Does the measure achieve its stated aim? (e.g., does a green‑belt actually prevent sprawl?)
• Distributional impacts – Who benefits and who may be disadvantaged?
• Long‑term sustainability – Does it reduce carbon emissions, improve climate‑resilience and support economic vitality?
• Trade‑offs – Higher densities can increase housing supply but may raise living costs if not managed.

6. Systems Perspective on Cities

A city can be viewed as an input‑process‑output system with feedback loops.

• Inputs: people, capital, resources (water, energy, food), information.
• Processes: production, services, transport, governance, cultural activities.
• Outputs: goods, services, waste, emissions, cultural products.
• Feedback loops: policy responses, market adjustments, community activism that modify future inputs and processes.

Understanding these loops explains why a single intervention (e.g., a new metro line) can have ripple effects across housing, employment and environmental outcomes.

7. Key Concepts for Assessment (AO1‑AO3)

• Define and differentiate: global, national, regional, local and primate cities.
• Describe typologies of urban growth: urbanisation, suburbanisation, sprawl, counter‑urbanisation, re‑urbanisation.
• Explain how economic, demographic, political/historical, technological and globalisation drivers operate at local, national and global scales, using contrasting case studies (LIC, MIC, HIC).
• Analyse the hierarchical structure of urban areas and the implications for resource allocation, transport and service provision.
• Interpret population‑growth equations and apply quantitative data (urban‑growth rates) to model expansion.
• Explain horizontal vs. vertical development, CBD functions, land‑use zones and residential zonation patterns.
• Evaluate sustainable‑development strategies, weighing effectiveness, equity and long‑term resilience.
• Apply a systems lens to illustrate inputs, processes, outputs and feedback in an urban context.

8. Suggested Diagram (for revision)