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Urbanisation is one of the most significant global processes of the twenty-first century. For the first time in human history, more than half the world's population lives in urban areas — a threshold crossed in 2007 according to the United Nations. Understanding the causes, patterns, and consequences of urbanisation is fundamental to the study of contemporary urban environments.
Key Definition: Urbanisation is the increase in the proportion of a country's population living in urban areas. It is distinct from urban growth, which refers to the absolute increase in the number of people living in cities.
The pace of urbanisation over the past two centuries has been extraordinary:
| Year | World Urban Population (%) | Total Urban Population |
|---|---|---|
| 1800 | ~3% | ~30 million |
| 1900 | ~14% | ~220 million |
| 1950 | ~30% | ~750 million |
| 2000 | ~47% | ~2.9 billion |
| 2007 | ~50% | ~3.3 billion (tipping point) |
| 2020 | ~56% | ~4.4 billion |
| 2050 (projected) | ~68% | ~6.7 billion |
The UN World Urbanization Prospects (2018 revision) projects that virtually all net population growth between 2020 and 2050 will be absorbed by urban areas, predominantly in Africa and Asia.
Exam Tip: Always distinguish between the rate of urbanisation (how quickly the proportion changes) and the level of urbanisation (the current proportion). HICs have high levels but low rates; LICs have lower levels but much higher rates. Examiners reward precise use of these terms.
Urbanisation is driven by two principal mechanisms: rural-to-urban migration and natural increase within cities.
Migration is the dominant driver of urbanisation in most developing countries. It is explained through push-pull theory, first formalised by Ravenstein (1885) in his "Laws of Migration":
| Push Factors (Rural) | Pull Factors (Urban) |
|---|---|
| Agricultural mechanisation reducing labour demand | Employment opportunities in manufacturing and services |
| Land fragmentation and declining farm size | Higher wages and better working conditions |
| Environmental degradation, drought, desertification | Access to education, healthcare, and social services |
| Lack of infrastructure and services | Perceived better quality of life |
| Conflict and insecurity | Cultural attractions and social networks |
Lee (1966) refined this model by introducing intervening obstacles (distance, cost, immigration controls) and personal factors (age, education, family ties) that mediate migration decisions. Lee argued that migration is selective — it disproportionately involves young, economically active adults, which has profound implications for both source and destination areas.
In many rapidly urbanising countries, natural increase (birth rate minus death rate) contributes significantly to urban population growth. Young migrants have higher fertility rates, and urban areas often have lower mortality due to better healthcare access. In sub-Saharan Africa, natural increase accounts for approximately 60% of urban growth (UN-Habitat, 2016).
Urbanisation is closely linked to the demographic transition model (DTM), which describes how populations change as countries develop economically:
graph LR
A[Stage 1: High BR & DR<br>Low urbanisation<br>Pre-industrial] --> B[Stage 2: High BR, Falling DR<br>Rapid population growth<br>Early urbanisation]
B --> C[Stage 3: Falling BR & DR<br>Accelerating urbanisation<br>Rural-urban migration]
C --> D[Stage 4: Low BR & DR<br>High urbanisation 70-80%<br>Post-industrial]
D --> E[Stage 5: BR below DR<br>Counter-urbanisation<br>Population decline]
Countries in Stages 2 and 3 of the DTM experience the most rapid urbanisation. This includes much of sub-Saharan Africa (Stage 2) and South/Southeast Asia (Stage 3). Countries in Stage 4 and 5 — most of Europe, Japan, South Korea — have largely completed the urbanisation process.
Key Definition: The demographic transition model describes the shift from high birth and death rates to low birth and death rates as a country develops. Urbanisation both drives and is driven by this transition.
A megacity is defined as a city with a population exceeding 10 million inhabitants. In 1970, there were just 3 megacities (Tokyo, New York, Osaka). By 2020, there were 34, and the UN projects 43 by 2030.
| Megacity | Country | Population (2020 est.) | Growth Type |
|---|---|---|---|
| Tokyo | Japan | 37.4 million | Stable/declining |
| Delhi | India | 30.3 million | Rapid growth |
| Shanghai | China | 27.1 million | Rapid growth |
| São Paulo | Brazil | 22.0 million | Moderate growth |
| Mumbai | India | 20.4 million | Rapid growth |
| Lagos | Nigeria | 14.4 million | Very rapid growth |
| London | UK | 9.3 million | Below threshold |
The geography of megacities has shifted dramatically. In 1950, seven of the world's ten largest cities were in the developed world. By 2025, only two (Tokyo and New York) will remain in the top ten.
The concept of the world city (or global city) was developed by Friedmann (1986) in his "World City Hypothesis" and refined by Sassen (1991) in her influential book The Global City. World cities are defined not by population size but by their role in the global economy:
Sassen identified New York, London, and Tokyo as the three pre-eminent global cities. The Globalization and World Cities Research Network (GaWC) at Loughborough University classifies world cities into tiers: Alpha++ (London, New York), Alpha+ (Hong Kong, Singapore, Tokyo, Shanghai, Paris), and lower tiers.
Exam Tip: Do not confuse megacities with world cities. Lagos is a megacity but is not typically classified as an Alpha world city. London is a world city but falls just below the megacity threshold. The concepts measure different things — population size versus global economic function.
Africa is the least urbanised continent (~43% urban in 2020) but has the fastest rate of urbanisation. The urban population is projected to triple between 2020 and 2050. Lagos, Kinshasa, Dar es Salaam, and Luanda are among the fastest-growing cities globally. Much of this growth is characterised by informal settlements and a lack of infrastructure investment.
Asia contains the largest absolute number of urban dwellers. China's urbanisation rate rose from 18% in 1978 to over 64% in 2020, representing the largest rural-to-urban migration in human history — an estimated 300 million people moved to cities between 1980 and 2015. India's urbanisation (~35% in 2020) is lower but accelerating.
Latin America is the most urbanised developing region (~81% urban in 2020), comparable to Europe. Much of this urbanisation occurred rapidly between 1950 and 1990, producing characteristic patterns of primacy (dominance by a single city, such as Buenos Aires, Lima, or Mexico City) and extensive informal settlements.
These regions are highly urbanised (75–83%) with low or negative rates of urbanisation. The dominant processes are now counter-urbanisation, suburbanisation, and re-urbanisation rather than primary urbanisation.
Urban primacy occurs when a country's largest city is disproportionately larger than other cities. The primate city rule, proposed by Jefferson (1939), states that a primate city is at least twice the size of the second-largest city.
Examples of urban primacy:
In contrast, Zipf (1949) proposed the rank-size rule, which states that the population of a city ranked nth in a country will be 1/n of the population of the largest city. This produces a log-linear distribution when plotted. Countries with well-developed urban systems, such as the USA and Germany, tend to approximate the rank-size rule more closely than countries with strong primacy.
Rapid urbanisation, particularly in LICs and NEEs, creates both opportunities and challenges:
| Opportunities | Challenges |
|---|---|
| Economic growth and agglomeration economies | Overcrowding and housing shortages |
| Access to education and healthcare | Growth of informal settlements/slums |
| Social mobility and cultural exchange | Inadequate water supply and sanitation |
| Innovation and entrepreneurship | Traffic congestion and air pollution |
| More efficient service provision | Unemployment and underemployment |
| Political representation | Crime, inequality, and social tension |
The UN estimates that approximately 1 billion people currently live in slums or informal settlements globally, a figure projected to rise to 2 billion by 2030 without significant intervention.
Exam Tip: When discussing consequences of urbanisation, always provide place-specific examples and data. A generic answer about "pollution" is far less effective than citing specific air quality data from Delhi (PM2.5 levels exceeding 500 μg/m³ during winter smog events, against a WHO guideline of 5 μg/m³).
| Concept | Key Detail |
|---|---|
| Urbanisation definition | Increase in proportion of population living in urban areas |
| Global tipping point | 2007 — more than 50% urban |
| Causes | Rural-to-urban migration (Ravenstein 1885, Lee 1966) and natural increase |
| Megacities | Population > 10 million; 34 in 2020; shifting to Global South |
| World cities | Friedmann 1986, Sassen 1991; defined by economic function, not size |
| Primacy | Jefferson 1939; primate city at least 2x the second city |
| Rank-size rule | Zipf 1949; city rank × population = constant |
| Key projection | 68% of world population urban by 2050 (UN) |