Urbanisation Trends and Patterns

Global Urbanisation Trends

The Urban Transition

Urbanisation is the increasing proportion of a national population living in urban areas. The global urban population exceeded the rural population for the first time in 2007. As of 2023, approximately 57% of the world's population (4.4 billion people) lives in urban areas, and the UN projects this will reach 68% by 2050.

The rate of urbanisation varies dramatically by region:

Region	Urban Population (%)	Annual Urbanisation Rate (%)	Projected 2050 (%)
North America	83	0.3	87
Latin America and Caribbean	82	0.4	87
Europe	75	0.2	80
Oceania	68	0.5	73
Asia	52	1.5	64
Africa	44	3.4	56

The most rapid urbanisation is occurring in Sub-Saharan Africa and South Asia. Africa's urban population is projected to triple between 2023 and 2050, adding approximately 900 million urban residents. This rapid growth frequently outpaces the capacity of governments and infrastructure to accommodate new residents, resulting in the proliferation of informal settlements, inadequate water and sanitation, and environmental degradation.

Components of Urban Growth

Urban population growth results from three components:

1. Natural increase: births minus deaths within urban areas. In many developing-country cities, high fertility rates among recent migrants (who tend to be young adults of reproductive age) contribute significantly to urban growth. Natural increase accounts for approximately 60% of urban population growth in Sub-Saharan Africa.
2. Rural-urban migration: the movement of people from rural to urban areas, driven by push and pull factors. This is the dominant component in many rapidly urbanising countries in Asia and Latin America.
3. Reclassification: as rural settlements grow and cross the threshold defined as "urban" (which varies by country), their populations are reclassified. In China, the relaxation of the hukou (household registration) system has accelerated the reclassification of rural migrants as urban residents. Reclassification can account for a significant proportion of apparent urbanisation, particularly in countries with low urban thresholds.

Urbanisation in Developed vs Developing Countries

Developed countries. Most developed countries have already completed their urban transition (urban population exceeds 75%). Current urbanisation rates are low (typically below 0.5% per year). Some cities in developed countries are experiencing population decline (urban shrinkage), particularly in deindustrialising regions (Detroit, USA; Liverpool, UK; the Ruhr region, Germany). Counter-urbanisation (the movement of people from large cities to smaller towns and rural areas, driven by lower housing costs, telecommuting, and environmental preferences) has been observed in many Western European countries since the 1970s.

Developing countries. The majority of future urban growth will occur in developing countries. The UN projects that by 2050, approximately 90% of the global urban population will live in Africa and Asia. The pace and scale of urbanisation in developing countries are unprecedented: cities such as Lagos (projected to reach 25 million by 2050), Kinshasa (20 million), and Dhaka (22 million) are growing by several hundred thousand residents per year.

Megacities

Definition and Distribution

A megacity is typically defined as an urban agglomeration with a population exceeding 10 million. As of 2023, there are 33 megacities worldwide. By 2050, the number is projected to reach approximately 43.

The distribution of megacities has shifted markedly. In 1950, only New York and Tokyo qualified as megacities, both in developed countries. By 2023, the majority of megacities are in developing countries, predominantly in Asia and increasingly in Africa.

Megacity	Country	Population (2023, millions)
Tokyo	Japan	37
Delhi	India	33
Shanghai	China	29
Dhaka	Bangladesh	23
Sao Paulo	Brazil	22
Mexico City	Mexico	22
Cairo	Egypt	22
Mumbai	India	22
Beijing	China	21
Osaka-Kobe	Japan	19

Characteristics and Challenges

Megacities share certain characteristics:

• Functional complexity: they are national or regional economic hubs, concentrating finance, commerce, government, and cultural functions.
• Spatial extent: megacity boundaries often extend across multiple administrative jurisdictions, complicating governance. The Tokyo metropolitan area encompasses approximately 13 500 km$^2$ and includes parts of three prefectures.
• Infrastructure challenges: transport congestion, inadequate housing, water supply deficits, air pollution, and waste management are endemic.
• Social diversity: megacities attract migrants from diverse origins, creating complex social mosaics and sometimes ethnic or religious spatial segregation.

Advantages of megacities: agglomeration economies (the productivity gains from firms and workers being located in close proximity, including shared infrastructure, labour market pooling, and knowledge spillovers); cultural and educational facilities; concentration of investment and employment opportunities.

Disadvantages: congestion costs (estimated at 2--4% of GDP in many megacities); inequality (spatial segregation of rich and poor, with informal settlements adjacent to affluent districts); environmental degradation; vulnerability to natural hazards (megacities in earthquake zones, coastal zones, and floodplains face elevated risk).

World Cities and Primate Cities

World Cities (Global Cities)

World cities are urban centres that function as nodes in the global economic network. They are distinguished by their economic, political, and cultural influence, not by population size alone. Saskia Sassen's (1991) concept of the "global city" emphasises the role of these cities as command centres for the global economy, housing the headquarters of transnational corporations, major financial institutions, and advanced producer services (legal, accounting, advertising, consulting).

The Globalisation and World Cities (GaWC) Research Network classifies cities based on their connectivity in producer services:

• Alpha++: London, New York
• Alpha+: Tokyo, Paris, Hong Kong, Shanghai, Beijing, Dubai, Singapore
• Alpha: Sydney, Mumbai, Milan, Chicago, Mexico City, Toronto, and others

World cities exhibit specific characteristics: a high concentration of corporate headquarters; major international airports and transport hubs; cultural institutions (universities, museums, media); diverse, multicultural populations; and significant political influence.

Primate Cities

A primate city is a city that is disproportionately large relative to other cities in the same country. The primacy ratio is the population of the largest city divided by the population of the second-largest city. A ratio exceeding 2:1 is generally considered to indicate primacy.

Country	Primate City	Second City	Primacy Ratio
Thailand	Bangkok (10.5 million)	Chiang Mai (0.13 million)	81:1
Peru	Lima (10.9 million)	Arequipa (1.0 million)	11:1
France	Paris (11.0 million)	Lyon (1.7 million)	6.5:1
UK	London (9.5 million)	Birmingham (2.6 million)	3.7:1

Causes of primacy. Primate cities often result from colonial history (colonial powers concentrated administration, trade, and infrastructure in a single port city), economic geography (agglomeration economies attract further investment to the largest city), political centralisation (unitary states with concentrated decision-making tend to produce primate cities), and physical geography (a single natural harbour or fertile plain may support one dominant urban centre).

Consequences of primacy. Positive: efficiency of concentrating resources and infrastructure in one node; strong national and international connectivity. Negative: regional inequality (resources drained from peripheral regions); rural-urban migration pressure; overconcentration of population and economic activity; vulnerability to natural disasters or terrorist attacks affecting the single dominant city.

Urban-Rural Migration

Push and Pull Factors

Rural-urban migration is driven by a combination of push factors (conditions that discourage remaining in rural areas) and pull factors (conditions that attract migrants to urban areas).

Push factors:

• Economic: low agricultural incomes, mechanisation reducing labour demand, land fragmentation through inheritance, seasonal unemployment, lack of non-farm employment opportunities
• Social: limited access to education and healthcare, social constraints (caste, gender), limited marriage prospects
• Environmental: soil degradation, desertification, drought, flooding, desert locust outbreaks
• Political: conflict, displacement, forced relocation

Pull factors:

• Economic: higher wages (urban-rural wage differentials can be 2--10x in developing countries), greater variety of employment opportunities, informal sector livelihoods
• Social: access to education (schools, universities), healthcare facilities, cultural amenities, entertainment
• Perceptual: the "bright lights" effect, media portrayals of urban life, aspirations for modernity

The Harris-Todaro Model

The Harris-Todaro model (1970) explains rural-urban migration in developing countries by noting that migration is driven not by actual urban wages but by expected urban wages, which account for the probability of obtaining formal employment:

$E(W_u) = W_u \cdot P_e$

where $E(W_u)$ is the expected urban wage, $W_u$ is the formal sector urban wage, and $P_e$ is the probability of obtaining formal employment (approximately equal to the formal sector employment rate). Even if $W_u$ exceeds the rural wage, if $P_e$ is low (due to high urban unemployment), migration may still be economically rational if:

$W_u \cdot P_e \gt W_r$

This model explains why urban unemployment can coexist with continued rural-urban migration: migrants are willing to accept the risk of unemployment in the informal sector because the expected income (including informal sector earnings) exceeds the certain rural wage.

Common Pitfalls: Assuming All Urban Growth is Due to Migration

A frequent error in examination responses is to attribute urban growth solely to rural-urban migration. In reality, natural increase accounts for a substantial and often dominant share of urban population growth, particularly in Sub-Saharan Africa (approximately 60% of urban growth) and parts of South Asia. Reclassification also contributes significantly in some countries. When analysing urbanisation trends, always identify and quantify the relative contributions of natural increase, migration, and reclassification where data are available.

Case Study: Lagos, Nigeria

Lagos is Africa's largest city and one of the fastest-growing megacities in the world. Its population has grown from approximately 1.4 million in 1960 (Nigerian independence) to approximately 16 million in 2023 (metropolitan area), and is projected to reach approximately 25 million by 2050.

Drivers of growth. Rural-urban migration from across Nigeria and neighbouring West African countries is driven by economic opportunity (Lagos accounts for approximately 25% of Nigeria's GDP), perceived access to education and healthcare, and the concentration of media, entertainment, and cultural industries. Natural increase contributes approximately 3% per year. The petroleum industry (Nigeria is Africa's largest oil producer) has concentrated corporate headquarters and associated services in Lagos.

Challenges. Approximately 60--70% of Lagos's population lives in informal settlements, the largest of which is Makoko (an estimated 100 000--250 000 people living on stilts over the Lagos Lagoon). Infrastructure is grossly inadequate: the road network was designed for approximately 2 million people; traffic congestion costs the Lagos economy an estimated NGN 8 billion (approximately USD 20 million) daily. Only approximately 10% of solid waste is properly collected; the remainder is dumped in waterways or unregulated landfills. Flooding is a recurrent problem due to inadequate drainage, blocked waterways, and the city's low-lying coastal location.

Responses. The Lagos State government has invested in Bus Rapid Transit (BRT Lite), which carries approximately 200 000 passengers per day along dedicated bus lanes; the Eko Atlantic project, a 10 km$^2$ development on reclaimed land intended as a high-value financial district; and various slum upgrading and clearance programmes. However, upgrading programmes have been criticised for prioritising the interests of developers and affluent residents over those of existing informal settlement communities.

For related topics, see ./urban-environmental-quality and ./urban-planning-and-sustainability. The parent topic page is at ../urban-environments.