Urban Environments

Urbanisation Trends

Global Patterns

Urbanisation is the process by which an increasing proportion of a population lives in urban areas. In 2007, for the first time in human history, more people lived in urban areas than in rural areas. As of 2023, approximately 57% of the global population (4.4 billion people) is urban, and this proportion is projected to reach 68% by 2050.

Urbanisation rates vary significantly by region and by level of economic development:

Region	Urban Population (%)	Urbanisation Rate (annual % change)
North America	83	0.3
Latin America and Caribbean	82	0.4
Europe	75	0.2
Oceania	68	0.5
Asia	52	1.5
Africa	44	3.4

The most rapid urbanisation is occurring in Sub-Saharan Africa and South Asia, where urban populations are growing at rates of 3--4% per year. This rapid growth often outpaces the capacity of governments to provide infrastructure, housing, and services, resulting in the proliferation of informal settlements.

Causes of Urbanisation

Rural-urban migration. Push factors from rural areas include: mechanisation of agriculture (reducing labour demand), land fragmentation through inheritance, environmental degradation (soil erosion, desertification), lack of educational and healthcare facilities, and low wages. Pull factors to urban areas include: employment opportunities in manufacturing and services, higher wages, access to education and healthcare, and the perceived attractions of urban lifestyle.

Natural increase. Urban populations grow not only through migration but also through natural increase (births minus deaths). In many developing-country cities, high fertility rates among recent migrants contribute to rapid population growth.

Reclassification. As rural areas develop and their populations reach urban thresholds, they are reclassified as urban. This administrative reclassification can account for a significant proportion of reported urbanisation, particularly in China and India.

Counter-urbanisation and re-urbanisation. In some developed countries, urbanisation has been partially reversed by counter-urbanisation (the movement of people from urban to rural areas, driven by factors such as lower housing costs, environmental quality, and telecommuting). More recently, some cities have experienced re-urbanisation (the return of population to inner urban areas, driven by regeneration, cultural amenities, and employment opportunities).

Urban Models

Urban models are simplified representations of the spatial structure of cities. They are useful analytical tools but should be treated as ideal types rather than accurate descriptions of any particular city.

The Burgess Concentric Zone Model (1925)

Ernest Burgess proposed that cities grow outward from a central business district (CBD) in a series of concentric rings:

1. CBD: the commercial and administrative centre; high land values; intensive land use
2. Transition zone (zone of transition): characterised by mixed industrial and residential land use; high population density; deteriorating housing; high crime rates; immigrant communities
3. Working-class zone: modest housing; industrial workers; relatively dense
4. Residential zone: middle-class housing; better quality; lower density
5. Commuter zone: affluent suburbs; low density; high car ownership

Limitations. The Burgess model assumes a uniform plain, equal accessibility in all directions, and a single CBD. It was developed based on Chicago in the 1920s and does not account for physical barriers (rivers, hills), multiple nuclei, transport corridors, or the spatial segregation of ethnic groups.

The Hoyt Sector Model (1939)

Homer Hoyt modified the Burgess model by proposing that cities grow in sectors (wedges) radiating from the CBD, rather than in concentric rings. Hoyt argued that high-rent residential areas expand outward along transport corridors (railways, main roads), while industrial areas expand along railways and waterways. Low-rent areas occupy the interstices between sectors.

Key insight: the sector model explains the persistence of social-class spatial patterns over time, as areas of similar land use tend to expand outward along established corridors rather than forming new concentric rings.

The Harris and Ullman Multiple Nuclei Model (1945)

Chauncy Harris and Edward Ullman proposed that cities develop around multiple centres (nuclei) of specialised activity, rather than a single CBD. Each nucleus attracts related activities, and the city grows through the expansion and merger of these specialised districts.

Common nuclei include: the CBD, port/industrial areas, university district, outlying business centres, residential suburbs, and industrial parks.

Strengths. The multiple nuclei model is more realistic than the Burgess or Hoyt models because it accommodates the complexity of modern cities with multiple centres of activity, transport networks, and specialised zones.

Model	Year	Structure	Key Assumption	Best Applied To
Burgess	1925	Concentric rings	Uniform plain, single CBD	Pre-automobile cities (e.g., 1920s Chicago)
Hoyt	1939	Sectors along transport corridors	Growth along lines of least resistance	Cities with strong transport corridors (e.g., railway-era London)
Harris and Ullman	1945	Multiple nuclei	Specialised centres of activity	Large, complex modern cities (e.g., Los Angeles, Tokyo)

Common Pitfalls: Applying Urban Models to Developing-Country Cities

All three classical urban models were developed based on cities in high-income countries and may not accurately represent the spatial structure of cities in low- and middle-income countries. Developing-country cities often feature: a colonial CBD (with modern commercial functions adjacent to informal settlements), extensive informal economies that do not conform to formal land-use zoning, rapid peripheral growth (often unplanned), and ethnic or religious spatial segregation. When applying these models to developing-country cities, identify the features that fit and those that do not, and explain the discrepancies.

Megacities and World Cities

Megacities

A megacity is typically defined as a city with a population exceeding 10 million. As of 2023, there are 33 megacities worldwide, the majority of which are in Asia and Africa. The largest megacities are Tokyo (37 million), Delhi (33 million), Shanghai (29 million), Dhaka (23 million), and Sao Paulo (22 million).

Characteristics of megacities:

• Scale: enormous populations and spatial extent (Tokyo's metropolitan area extends over 13 500 km$^2$)
• Functional complexity: megacities are national or regional economic hubs, concentrating finance, commerce, media, and government functions
• Infrastructure challenges: transport congestion, inadequate housing, water supply and sanitation deficits, air pollution
• Social diversity: megacities attract migrants from diverse regional and national origins, creating complex social mosaics

World Cities

World cities (or global cities) are urban centres that function as nodes in the global economic network. They are distinguished not by population size but by their economic, political, and cultural influence. Friedmann's (1986) "World City Hypothesis" identified key world cities based on their role in linking national economies to the global economy.

The Globalisation and World Cities (GaWC) Research Network classifies cities into Alpha (++/+), Beta (+/+), and Gamma (+/+/-) categories based on their connectivity in producer services (accountancy, advertising, banking, law). London and New York are consistently ranked as Alpha++ cities; Tokyo, Paris, Hong Kong, Shanghai, Beijing, Dubai, and Singapore are Alpha+ cities.

Characteristics of world cities:

• Headquarters of major TNCs and financial institutions
• Major international airports and transport hubs
• Cultural institutions (museums, universities, media organisations)
• Diverse, multicultural populations
• Significant political influence (hosting international organisations, national governments)

Urban Problems

Housing

The global housing deficit is estimated at approximately 1.6 billion units, with the most acute shortages in rapidly urbanising developing countries. In cities such as Lagos, Dhaka, and Mumbai, a significant proportion of the population lives in informal settlements lacking basic services (water, sanitation, electricity).

Transport

Urban transport problems include congestion (estimated to cost the UK economy approximately £8 billion per year in lost productivity), air pollution from vehicle emissions, inadequate public transport systems, and spatial mismatch between residential areas and employment centres.

Pollution

Air pollution is a major urban health hazard. The WHO estimates that outdoor air pollution causes approximately 4.2 million premature deaths annually. Cities with the highest levels of particulate matter (PM2.5) include Delhi, Lahore, Dhaka, and Cairo. Vehicle emissions, industrial activity, construction dust, and the burning of biomass are the primary sources.

Water pollution from untreated sewage, industrial effluent, and agricultural runoff contaminates water supplies in many developing-country cities. Only approximately 56% of urban wastewater in developing countries is treated, compared to approximately 80% in developed countries.

Crime and Inequality

Urban crime rates vary enormously by city, neighbourhood, and type of crime. Spatial inequality -- the concentration of poverty in specific neighbourhoods, often spatially segregated by race, ethnicity, or class -- is a persistent feature of cities in both developed and developing countries. Gini coefficients within cities are often higher than national averages: in Sao Paulo, the Gini coefficient exceeds 0.6, compared to Brazil's national Gini of approximately 0.53.

Informal Economy

The informal economy (economic activity that is not regulated, taxed, or protected by the state) is a major source of employment in developing-country cities, accounting for an estimated 60--80% of total employment in Sub-Saharan Africa and South Asia. While the informal economy provides livelihoods that would otherwise not exist, it is characterised by low wages, insecurity, and absence of legal protections.

Urban Solutions

Sustainable Cities

The concept of sustainable urban development seeks to balance economic growth, social equity, and environmental protection. Key principles include:

• Compact city design: high-density, mixed-use development that reduces the need for car travel and preserves greenfield land
• Green infrastructure: urban parks, green roofs, urban forests, and wetlands that provide ecosystem services (stormwater management, air quality improvement, heat island mitigation)
• Renewable energy: solar panels, wind turbines, and district heating systems that reduce dependence on fossil fuels
• Sustainable transport: public transit systems (bus rapid transit, light rail, metro), cycling infrastructure, pedestrian zones, and congestion pricing
• Water-sensitive urban design: rainwater harvesting, greywater recycling, permeable surfaces, and constructed wetlands for stormwater management

Smart Cities

Smart cities use digital technology and data analytics to improve urban governance, service delivery, and quality of life. Examples include:

• Singapore: extensive use of sensors and cameras for traffic management, environmental monitoring, and public safety; the Smart Nation initiative integrates data from multiple government agencies
• Barcelona: smart lighting (LED streetlights that adjust based on pedestrian presence), sensor-enabled waste management (bins signal when full), and digital participation platforms for citizen engagement
• Copenhagen: real-time bicycle traffic monitoring, smart grid energy management, and data-driven urban planning

Criticisms of smart cities. Privacy concerns (extensive surveillance and data collection), digital exclusion (marginalising residents without access to digital technology), and the risk of prioritising technological solutions over democratic participation and social justice.

Green Belts

A green belt is a ring of protected open land surrounding a city, intended to prevent urban sprawl by restricting development. London's Metropolitan Green Belt, established in 1938, covers approximately 514 000 hectares and restricts development around London's periphery.

Strengths: prevents urban sprawl, preserves agricultural land and ecosystems, maintains the distinct identity of settlements.

Limitations: can increase housing prices by restricting supply (London's green belt has been criticised for contributing to the city's housing affordability crisis); may push development to locations beyond the green belt, increasing commuting distances and associated emissions.

Public Transport Systems

Efficient public transport reduces congestion, air pollution, and carbon emissions. Notable examples include:

• Bus Rapid Transit (BRT): Curitiba, Brazil pioneered BRT in the 1970s. The system uses dedicated bus lanes, elevated stations with pre-board ticketing, and high-capacity articulated buses, achieving metro-like speeds at a fraction of the cost.
• Metro systems: cities such as Tokyo, London, Paris, and Shanghai have extensive metro networks that carry millions of passengers per day. Shanghai's metro, opened in 1993, is now the longest in the world (over 800 km of track).

Urban Renewal and Regeneration

Case Study: London Docklands

The London Docklands (the docks along the River Thames in East London) declined from the 1960s onward as containerisation rendered the docks obsolete and manufacturing moved to lower-cost locations. By the early 1980s, the area was characterised by derelict land, high unemployment, and population loss.

The London Docklands Development Corporation (LDDC), established in 1981, undertook a comprehensive regeneration programme:

• Infrastructure investment: the Docklands Light Railway (DLR) was extended, connecting the area to the City of London; the Jubilee Line extension opened in 1999.
• Commercial development: Canary Wharf was developed as a secondary financial district, attracting major banks and financial institutions.
• Residential development: former docklands were converted into high-value housing, and the population of the Docklands area increased from approximately 39 000 (1981) to over 120 000 (2023).
• Social impacts: the regeneration was criticised for displacing existing low-income communities (gentrification), creating a socially polarised area with high-value developments adjacent to deprived neighbourhoods, and prioritising commercial interests over community needs.

Case Study: Curitiba, Brazil

Curitiba (population approximately 1.9 million; metropolitan area approximately 3.7 million) is widely cited as a model of sustainable urban planning in a developing-country context.

Key features:

• Bus Rapid Transit (BRT): the Rede Integrada de Transporte (RIT) serves approximately 2.3 million passengers per day. Dedicated bus lanes, tube-like stations, and express routes achieve average speeds of 20--30 km/h, comparable to metro systems. The BRT costs approximately one-tenth of a metro system per kilometre.
• Land-use planning: Curitiba's Master Plan (1966) designated linear corridors of mixed-use, high-density development along the BRT axes, with lower-density zoning between corridors. This concentrated growth along transport routes and preserved green areas.
• Waste management: the "Garbage That Is Not Garbage" programme pays low-income residents in bus tokens or food for collecting recyclable materials, achieving a recycling rate of approximately 70%.
• Green space: Curitiba has approximately 52 m$^2$ of green space per inhabitant, one of the highest ratios in the world, achieved through the preservation of floodplains as parks and the creation of urban forests.

Limitations: Curitiba's model has been criticised for benefiting the formal city while excluding the metropolitan periphery, where approximately 1.8 million people live in informal settlements with inadequate services. The city's success also depended on strong political leadership (particularly under Mayor Jaime Lerner, 1971--1975, 1979--1984, 1989--1992) that may not be replicable in other contexts.

Case Study: Singapore

Singapore (population approximately 5.9 million on 733 km$^2$) exemplifies intensive urban planning in a high-density, resource-constrained city-state.

Key strategies:

• Housing: the Housing and Development Board (HDB) provides public housing for approximately 80% of the resident population. HDB towns are designed as self-contained neighbourhoods with schools, clinics, markets, and public transport.
• Transport: an extensive MRT (Mass Rapid Transit) rail network (over 200 km) complemented by bus services; an Electronic Road Pricing (ERP) system charges motorists for entering congested zones, managing demand.
• Water management: the "Four National Taps" strategy diversifies water supply through local catchment (17 reservoirs), imported water (from Malaysia), NEWater (recycled treated wastewater, supplying approximately 40% of demand), and desalination (providing approximately 25% of demand).
• Greening: despite high density, Singapore maintains approximately 47% green cover through parks, nature reserves, vertical greening (green walls and roofs), and the "City in a Garden" initiative.

Squatter Settlements

Characteristics

Squatter settlements (also called informal settlements, shanty towns, or bidonvilles) are residential areas where inhabitants have no legal claim to the land and where buildings do not comply with planning and building regulations. They are characterised by:

• Inadequate housing (impermanent materials such as corrugated iron, wood, plastic sheeting)
• Lack of basic services (piped water, sanitation, electricity, waste collection)
• Overcrowding (high population density)
• Insecurity of tenure (risk of eviction)
• Vulnerability to hazards (flooding, landslides, fire)

Case Study: Dharavi, Mumbai

Dharavi, located in central Mumbai, is one of Asia's largest informal settlements, with an estimated population of 600 000--1 000 000 people on approximately 2.4 km$^2$.

• Economy: Dharavi is not merely a residential slum; it is a major economic hub with an estimated annual turnover of US$1 billion. Industries include leather goods, pottery, recycling, garments, and food processing. The recycling industry alone processes waste from across Mumbai, employing approximately 250 000 people.
• Living conditions: despite its economic dynamism, living conditions in Dharavi are severely inadequate. Approximately 1 toilet serves 1400 people; water supply is intermittent; drainage is poor, leading to regular flooding during the monsoon season.
• Redevelopment plans: the Dharavi Redevelopment Project, first proposed in 2004, aims to replace the settlement with high-rise housing and commercial space. However, the plan has been repeatedly delayed due to disputes over compensation, the interests of existing residents, and the political influence of Dharavi's informal economy.

Case Study: Kibera, Nairobi

Kibera, located approximately 5 km southwest of Nairobi's CBD, is one of Africa's largest informal settlements, with an estimated population of 170 000--250 000 people (population estimates vary widely due to the absence of a formal census).

• Origins: Kibera originated in the early 20th century as a settlement for Nubian soldiers serving in the British colonial army. It grew rapidly after Kenyan independence in 1963 as rural migrants arrived in Nairobi seeking employment.
• Living conditions: the majority of residents live in single-room structures of mud, timber, and corrugated iron. Only approximately 20% of households have electricity; sanitation facilities are grossly inadequate (approximately 1 latrine per 50--100 people); water is purchased from private vendors at prices 5--10 times the municipal rate.
• Upgrading initiatives: the Kenya Slum Upgrading Programme (KENSUP), launched in 2004 with World Bank funding, aimed to improve infrastructure and housing in Kibera. Progress has been slow, and many residents have been sceptical of upgrading programmes that they fear will lead to rent increases or eviction.

Upgrading Strategies

Upgrading strategies for informal settlements include:

Strategy	Description	Advantages	Disadvantages
Site-and-service	Government provides plots with basic services (water, sanitation, roads); residents build their own housing	Low cost; respects residents' agency	Does not address existing overcrowding; may not reach the poorest
In-situ upgrading	Improving existing settlements with infrastructure, services, and tenure security	Minimises displacement; preserves social networks	Expensive in dense settlements; may increase land values (leading to gentrification)
Resettlement	Relocating residents to new housing on alternative sites	Can provide high-quality housing; allows comprehensive planning	Often far from employment; social disruption; resistance from residents
Regularisation	Granting legal tenure to informal settlers	Provides security of tenure; enables investment in housing	May increase land values; does not directly improve services

Common Pitfalls: Equating Informal Settlements with Poverty

Informal settlements are often associated with poverty, but the relationship is not straightforward. Many informal settlements are economically productive (Dharavi is a case in point), and many residents are employed in the formal economy but cannot afford formal housing. The informal economy that thrives in squatter settlements is often a significant contributor to urban GDP. Avoid characterising informal settlements as uniformly "backward" or "dysfunctional"; instead, analyse their functions, challenges, and the structural factors that produce them.

Urban Environmental Quality

Air Pollution

Urban air pollution is caused by vehicle emissions, industrial activity, construction, power generation, and the burning of biomass. Key pollutants include particulate matter (PM2.5 and PM10), nitrogen oxides ($\mathrm{NO_x}$), sulphur dioxide ($\mathrm{SO_2}$), carbon monoxide (CO), and ground-level ozone ($\mathrm{O_3}$).

Impacts: respiratory diseases (asthma, chronic obstructive pulmonary disease, lung cancer), cardiovascular disease, reduced visibility, ecosystem damage (acid deposition, eutrophication), and climate change.

Management strategies:

• Vehicle emissions standards: Euro 6 standards in the EU, Bharat Stage VI in India
• Low-emission zones (LEZs): London's Ultra Low Emission Zone (ULEZ), introduced in 2019, charges vehicles that do not meet emission standards
• Public transport investment: reducing private vehicle use through efficient and affordable public transport
• Green infrastructure: trees and vegetation absorb pollutants and reduce the urban heat island effect

Water Management

Urban water management faces three interrelated challenges: ensuring adequate water supply, treating wastewater, and managing stormwater.

• Water supply: many cities in water-scarce regions (Cape Town, Chennai, Mexico City) have experienced acute water crises. Strategies include rainwater harvesting, wastewater recycling, leak reduction in distribution networks (many cities lose 20--40% of treated water through leaks), and desalination.
• Wastewater treatment: secondary and tertiary treatment plants remove biological and chemical contaminants before discharge. Many developing-country cities lack adequate treatment capacity, resulting in the discharge of untreated sewage into waterways.
• Stormwater management: traditional urban drainage systems (concrete channels, underground pipes) are designed to channel stormwater away quickly but increase flood risk downstream. Sustainable urban drainage systems (SUDS) -- permeable surfaces, rain gardens, bioswales, green roofs -- slow and filter stormwater, reducing flood risk and improving water quality.

Waste Management

Urban waste generation is increasing globally, driven by rising consumption and population growth. The World Bank estimates that global waste generation will increase by 70% from 2016 levels by 2050, reaching 3.4 billion tonnes per year.

Management strategies (hierarchy of waste management):

1. Prevention: reducing waste generation through product design, regulation, and consumer behaviour change
2. Reuse: extending the life of products through repair, refurbishment, and second-hand markets
3. Recycling: recovering materials from waste for reprocessing
4. Recovery: extracting energy from waste through incineration or anaerobic digestion
5. Disposal: landfill (the least preferred option; methane emissions, leachate contamination, land consumption)

Developed countries typically rely on recycling and incineration; many developing countries depend on open dumping and open burning, with severe environmental and health consequences. Informal waste pickers play a critical role in recycling in many developing-country cities but often work under hazardous conditions and receive low prices for recovered materials.