Processes of urban growth

Urban Growth – Processes of Urban Growth (Cambridge A‑Level Geography 9696)

1. Definition & Scale of Analysis

• Urban growth – the increase in a city’s population and/or spatial extent over time.
• Examined at local, regional and global scales; the scale chosen influences the data required and the interpretation of causes and consequences.

2. Processes Driving Urban Growth

2.1 Demographic Processes

• Natural increase – births minus deaths within the urban population.
• Net migration – the balance of in‑migration (rural‑to‑urban, inter‑urban, international) and out‑migration.

Cambridge‑style exponential model:

$$P_t = P_0 e^{rt}$$

where P₀ = initial population, r = annual rate of natural increase, t = years. If r = 0.02 (2 % yr⁻¹), the population rises by ≈ 22 % in a decade.

2.2 Spatial (Area) Growth

• Measured as the increase in built‑up land or urban‑area extent (km²).
• Typical fast‑growing cities in the Global South show 5–10 % area growth per decade.

2.3 Types of Urban Growth

Growth type	Key characteristics	Typical drivers	Illustrative example
Urbanisation	Rapid rise in urban population and built‑up area.	Rural‑to‑urban migration, natural increase, economic pull.	Lagos, Nigeria
Suburbanisation	Movement from city centre to low‑density suburbs; often car‑dependent.	Housing demand, desire for larger homes, improved transport.	Greater London outer boroughs
Urban sprawl	Low‑density, peripheral expansion with fragmented land‑use.	High car ownership, cheap fringe land, lax planning.	Phoenix, USA
Counter‑urbanisation	People move from cities to rural or small‑town settings.	Telecommuting, lifestyle preference, housing affordability.	South‑west England (e.g., Devon)
Re‑urbanisation (urban renewal)	Return of population and investment to inner‑city areas; regeneration of derelict land.	Policy incentives, cultural amenities, gentrification.	London Docklands, Manchester’s Northern Quarter
Leap‑frog development	Discontinuous outward growth that leaves undeveloped gaps.	Speculative land‑markets, poor planning coordination.	Johannesburg’s peripheral townships

2.4 Urban Hierarchy

• Urban areas are organised in a hierarchy based on population size, economic functions and service provision.
• Primate city – a city that is > 2 times larger than the next biggest city and dominates national politics, culture and the economy (e.g., London in the UK, Bangkok in Thailand).
• World‑city categories – Alpha, Beta, Gamma cities (global financial, business and cultural hubs). Example: New York (Alpha), Nairobi (Beta).
• Understanding hierarchy helps explain why growth pressures are concentrated in certain cities while others stagnate.

3. Demographic & Migration Models

• Exponential growth model – shown above; useful for early‑stage urbanisation.
• Migration transition model – illustrates the shift from net out‑migration in early industrialisation to net in‑migration in later stages of development.

4. Spatial Processes of Urban Expansion

1. Concentric Zone Model (Burgess) – growth radiates outward in rings.
2. Sector Model (Hoyt) – development follows transport corridors, creating wedges.
3. Multiple Nuclei Model (Harris & Ullman) – several sub‑centres develop within the urban area.
4. Urban sprawl – low‑density peripheral expansion, often car‑dependent.
5. Leap‑frog development – discontinuous outward growth leaving undeveloped gaps.

4.1 Comparative Table of Urban Growth Models

Model	Core concept	Key drivers	Typical pattern	Limitations
Concentric Zone	City expands outward in rings.	Population pressure, transport costs.	Ring‑shaped land‑use zones.	Assumes uniform terrain; less relevant where modern transport reduces commuting costs.
Sector	Growth follows major transport routes.	Infrastructure, economic corridors.	Wedge‑shaped sectors radiating from centre.	Over‑emphasises transport; struggles with polycentric cities.
Multiple Nuclei	Several sub‑centres develop.	Specialised functions, decentralisation.	Patchwork of distinct nuclei.	Complex to map; may overlook hierarchical relationships.
Urban Sprawl	Low‑density peripheral expansion.	Car ownership, housing demand.	Diffuse, fragmented development.	Often unsustainable; ignores land‑use efficiency.
Leap‑frog	Discontinuous outward growth.	Speculative land markets, weak planning.	Isolated pockets of development with gaps.	Creates inefficient service provision and traffic patterns.

5. Urban Structure & Change (Systems Perspective)

Urban structure can be viewed as a system:

• Inputs – infrastructure (roads, rail, utilities), housing stock, labour force.
• Processes – land‑use allocation, residential location choice, economic activity location.
• Outputs – economic output, quality of life, environmental impacts.

5.1 Horizontal vs. Vertical Development

• Horizontal growth – outward spread of low‑rise housing estates, business parks and shopping centres.
• Vertical growth – high‑rise, mixed‑use towers; typical in dense city centres and emerging megacities (e.g., Shanghai, Dubai).

5.2 Land‑Use Zones & Residential Zonation

Key drivers of residential location decisions:

• Income level & housing affordability.
• Ethnic or cultural clustering.
• Proximity to employment and transport networks.
• Planning policies (density targets, green‑belt restrictions).

5.3 Place Identity & Perception of Place

Place identity is shaped by historic built‑environment, cultural landmarks and residents’ sense of belonging. Changes such as converting warehouses to loft apartments can attract new demographic groups and alter the perceived character of an area.

5.4 Changing Location of Activities

Activity	Traditional location	New location trend	Illustrative cities
Retail (high‑street)	City centre	Out‑of‑town shopping centres, retail parks.	Manchester (Trafford Centre) vs. Detroit (downtown revitalisation)
Manufacturing	Inner‑city industrial belts	Peripheral industrial parks, Special Economic Zones.	Shenzhen (high‑tech parks) vs. Glasgow (decline of traditional mills)
Knowledge‑based services	CBD financial districts	Mixed‑use “knowledge clusters” in regenerated docklands or university precincts.	London’s Tech City, Shanghai’s Pudong

6. Economic Processes Supporting Growth

• Industrialisation – factories, industrial parks, logistics hubs.
• Service‑sector expansion – finance, education, health, tourism, ICT.
• Foreign Direct Investment (FDI) – multinational headquarters, regional offices.
• Informal economy – street markets, micro‑enterprises; crucial for migrant livelihoods.

7. Role of Infrastructure

Transport, water, energy and communications networks lower travel costs, increase accessibility and stimulate both residential and commercial development. A simple relationship often used in A‑Level assessments is:

$$\text{Growth Rate} \propto \frac{1}{\text{Travel Time to CBD}}$$

Examples:

• Metro extensions in Shanghai accelerated high‑rise development around new stations.
• Ring roads around Birmingham (UK) promoted large suburban housing estates.

8. Policy Influences on Urban Growth

• New towns & satellite cities – planned settlements to relieve pressure on existing metropolises (e.g., Milton Keynes, China’s Tianjin Binhai).
• Zoning & density regulations – define land‑use categories, set maximum floor‑area ratios.
• Housing policies – public housing, subsidies, rent controls, “affordable‑housing” quotas.
• Environmental controls – green belts, flood‑plain restrictions, air‑quality zones.
• Regeneration incentives – tax reliefs, public‑private partnerships (PPP), heritage grants.

9. Sustainable Urban Development

9.1 Core Sustainability Pillars (Cambridge syllabus)

• Environmental – resource use, pollution, climate resilience.
• Social – equity, health, community cohesion.
• Economic – viability, employment, cost‑effectiveness.

9.2 Key Urban Sustainability Issues & Management Strategies

Issue	Typical urban problem	Hard (engineering) strategies	Soft (behavioural/ policy) strategies
Solid‑waste management	Overflowing landfills, illegal dumping.	Engineered sanitary landfills, waste‑to‑energy incinerators, mechanised collection.	Recycling schemes, community clean‑up programmes, pay‑as‑you‑throw tariffs.
Transport	Congestion, high CO₂ emissions.	Rapid transit (metro, BRT), congestion‑charging zones, dedicated bus lanes.	Travel‑plan incentives, car‑share schemes, promotion of walking/cycling.
Housing density & quality	Unaffordable housing, slum proliferation.	High‑rise public housing, compulsory purchase orders, modular construction.	Rent‑control, community‑led housing co‑ops, inclusionary‑housing policies.
Green space & water management	Loss of parks, flood risk.	Constructed wetlands, flood‑defence walls, sustainable drainage systems (SuDS).	Green‑belt preservation, urban greening schemes, community gardens.

9.3 Evaluation Framework (AO3)

When assessing any sustainability strategy, consider the following criteria:

1. Effectiveness – does it address the root cause of the problem?
2. Economic feasibility – cost‑benefit analysis, funding sources, long‑term maintenance.
3. Social equity – who benefits and who bears the costs?
4. Environmental side‑effects – unintended impacts (e.g., incineration reduces landfill but may increase air pollution).
5. Time‑scale – short‑term relief vs. long‑term resilience.

9.4 Comparative Case Studies

City	Key issue addressed	Hard strategies	Soft strategies	Evaluation (using framework)
Manchester, UK	Post‑industrial decline, transport congestion, brownfield regeneration.	Metrolink tram network; redevelopment of Salford Quays with mixed‑use towers; flood‑defence walls along River Irwell.	Skills‑training programmes; community‑led planning workshops; heritage‑preservation grants.	Positive: ↑ employment, ↑ property values, 12 % reduction in car trips. Negative: Gentrification displaced low‑income households; high public borrowing.
Johannesburg, South Africa	Urban sprawl, informal settlements, water scarcity.	Ring‑road upgrades; engineered storm‑water retention basins.	Informal‑settlement upgrading programmes; water‑saving public awareness campaigns; land‑use zoning to limit leap‑frog.	Effective at reducing informal settlement health risks; however, limited funding slowed full implementation and some sprawl persisted.

10. Skills Development (AO2)

• Interpreting data – population pyramids, urban‑area growth curves, migration tables.
• Map analysis – identify land‑use zones, growth patterns (concentric, sector, polycentric) and relate them to transport infrastructure.
• Graphical representation – plot % population growth per decade; compare natural increase vs. net migration.
• Evaluation practice – apply the AO3 framework to critique a given sustainability strategy.

11. Summary of Processes

1. Demographic change – natural increase and net migration.
2. Economic restructuring – industrialisation → service‑based economies, FDI, informal sector.
3. Infrastructure development – transport, utilities, communications.
4. Policy decisions – planning, housing, environmental controls.
5. Spatial patterns – concentric, sector, multiple nuclei, sprawl, leap‑frog.
6. Sustainability pressures – waste, transport, housing, green space; managed through hard/soft strategies and evaluated against environmental, social and economic criteria.

12. Key Terms

• Natural increase
• Net migration
• Urbanisation
• Suburbanisation
• Urban sprawl
• Counter‑urbanisation
• Re‑urbanisation / Urban renewal
• Leap‑frog development
• Polycentric city
• Primate city
• Urban hierarchy
• Green belt
• Foreign Direct Investment (FDI)
• Horizontal vs. vertical development
• Place identity
• Solid‑waste management
• Transport congestion
• Housing density
• Urban greening
• Hard vs. soft strategies
• Environmental, social and economic sustainability pillars

13. Suggested Diagrams for Revision

• Combined illustration of Concentric Zone, Sector and Multiple Nuclei models.
• Population growth curve with exponential fit (including natural increase vs. net migration).
• Hard/soft strategy matrix for the four sustainability issues.
• Urban hierarchy pyramid (hamlet → village → town → city → primate city).
• Cross‑section showing horizontal vs. vertical development in a dense Asian megacity.
• Map excerpt showing leap‑frog development and green‑belt boundaries.