Megacities: GCSE Geography Guide

What is a megacity and where are they found?

A megacity is defined as a metropolitan area with a population exceeding 10 million. The term is used in GCSE geography to distinguish the very largest cities from ordinary large cities (world cities) or simply large cities. Some geographers prefer the term metacity for cities over 20 million.

The distribution of megacities has shifted dramatically in recent decades. In 1975, the only megacities were Tokyo, New York and Mexico City. By 2024, 34 cities qualify, and the majority are in Asia, Africa and Latin America:

London does not quite qualify as a megacity by the standard definition (its metropolitan area is around 9 million), illustrating how megacity growth is concentrated outside Europe and North America.

Why are megacities growing in the Global South?

The rapid growth of megacities in low and middle income countries reflects urbanisation — the process by which an increasing proportion of a country's population lives in cities. Three processes drive this:

• Rural–urban migration: People move from countryside to cities seeking employment, higher wages, education and healthcare. The push factors include rural poverty, land scarcity, drought and lack of services; the pull factors include better wages, schools, hospitals and social networks.
• Natural increase: Populations within cities grow as birth rates exceed death rates — cities often have younger age profiles than rural areas.
• Reclassification: As smaller towns grow, they reach the threshold size to be reclassified as cities.

The shift of megacity growth to the Global South reflects the fact that the UK, the US and Western Europe urbanised during the Industrial Revolution (nineteenth and early twentieth centuries). Developing countries are urbanising now, often faster than the Global North did, and without the same levels of infrastructure investment.

What opportunities do megacities offer?

Megacities generate agglomeration economies — the economic benefits that come from having many businesses, workers, consumers and institutions concentrated in one place. These include:

• A large pool of workers with diverse skills
• Proximity to suppliers, customers and competitors, reducing transport costs
• Access to specialised services (banking, legal, design) that only exist in large cities
• Knowledge spillovers — ideas spreading between firms and individuals

For migrants from rural areas, cities typically offer higher wages, better access to healthcare and schools, and more diverse social opportunities. Even megacities in low-income countries tend to have better health and education outcomes than the rural areas people have left.

What challenges do megacities face?

The scale of megacity growth creates challenges that can overwhelm governments and infrastructure:

Informal settlements: In megacities in the Global South, between 30% and 70% of residents may live in informal settlements (slums), characterised by self-built housing, insecure land tenure, limited access to water and sanitation, and high population density. Dharavi in Mumbai (approximately 700,000–1 million people in just 2.4 km²) is one of the world's most studied slums. Residents of informal settlements are often excluded from the formal economy and public services.

Traffic and congestion: The sheer volume of people and vehicles in megacities creates extreme congestion. Lagos and Jakarta frequently appear in surveys of the world's worst traffic. Air pollution from vehicles is a major public health issue in cities like Delhi, where particulate pollution exceeds WHO safe limits on most days of the year.

Water and sanitation: Providing clean water and sewage treatment to tens of millions of people is enormously expensive and technically demanding. Many megacities have significant populations with no access to piped water (relying on informal vendors at much higher cost) or flush toilets.

Governance: Managing a megacity requires coordinated action across housing, transport, water, electricity, planning and social services. Many megacities straddle multiple administrative boundaries, making coordination difficult. Corruption and under-funding are common problems.

How do HIC and LMIC megacities compare?

The experience of living in a megacity differs enormously between high-income and low-income countries.

Tokyo is the world's largest megacity but manages with extraordinary efficiency. The metropolitan rail network carries over 40 million passenger journeys per day. Flooding is managed by a vast underground drainage system. Crime rates are very low. Air quality meets international standards. Tokyo demonstrates that very large urban populations can be managed successfully — but it required decades of investment and a strong governance tradition.

Dhaka (Bangladesh) and Lagos (Nigeria) face the same population scales with a fraction of Tokyo's resources. Infrastructure barely keeps pace with growth; informal settlements expand faster than governments can provide services. This is not a failure of the people who live in these cities — it reflects the resource gap between rich and poor countries.

Frequently asked questions

What is the difference between a megacity, a world city and a primate city?

A megacity is simply a city over 10 million population — a population threshold. A world city (or global city) is a city that plays a key role in the global economy through finance, business services, media and culture — London, New York and Tokyo are world cities regardless of population. A primate city is a city that is disproportionately large compared to other cities in the same country — Paris, for example, is more than six times the size of France's second city, Lyon. A city can be all three (Tokyo), some (Lagos is a megacity and primate city but not yet a world city in the full sense) or just one.

Why is Delhi growing so fast?

Delhi is projected to become the world's most populous city by the late 2020s. Its growth reflects India's overall urbanisation: hundreds of millions of people are moving from rural to urban areas as India industrialises and its service economy grows. Delhi's role as the national capital, its large government and business sector, and its position as a transport hub attract migrants from across northern India. Rural poverty and lack of employment in the countryside are the push factors; Delhi's relatively higher wages and services are the pull factors.

Can megacities be sustainable?

Sustainability in megacities is achievable but requires deliberate investment and governance. Dense cities are actually more energy efficient per capita than sprawling suburban cities — public transport is more viable, buildings share walls, and distances are shorter. Singapore (not itself a megacity by population) demonstrates that dense urban environments can be well-governed, green and liveable. Tokyo shows that a megacity can function well with strong institutions. The challenge is that the fastest-growing megacities in the Global South face rapid growth without the institutional capacity and infrastructure funding that Tokyo and Singapore had.

What is the difference between urbanisation and suburbanisation?

Urbanisation is the process of increasing proportions of a population living in urban areas — typically from rural to urban movement. It is measured as the percentage of a country's population in urban areas. Suburbanisation is a different process: the movement of people and businesses from city centres to the outer edges of urban areas, creating low-density suburbs. It happened extensively in the UK and USA in the mid-twentieth century as car ownership increased. Counter-urbanisation is when people move from cities entirely to smaller towns and rural areas. These three processes often happen simultaneously in different parts of the same country.

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