World Cities, Megacities, and Megalopolises

A world (or global) city is a city that serves as a major node in the global economy, with a concentration of corporate headquarters, finance and advanced services; a megacity is a city with more than 10 million inhabitants; and a megalopolis is a chain of metropolitan areas that have grown together into one huge urban region. In brief: New York, London and Tokyo are the classic world cities. The United Nations counted 33 megacities in 2018, most of them in Asia, and expects the number to rise to about 43 by 2030. The best-known megalopolis, named by Jean Gottmann in 1961, is the northeastern seaboard of the United States from Boston to Washington, DC, often called Boswash.

These three types of urban region overlap but describe different things: influence, size and the form of urban growth. This guide defines each concept, explains how they are measured and where they are found, discusses their opportunities and challenges, compares them in a table, works through example calculations, outlines the history and corrects common mistakes.

What are world cities?

The idea of a world city was discussed by Peter Hall in 1966 and developed by John Friedmann in 1986. The sociologist Saskia Sassen’s book The Global City (1991) argued that New York, London and Tokyo are command centers of the world economy, with the headquarters of multinational firms, global banks, stock exchanges and specialist services such as law, accounting, advertising and consulting. Such cities are linked by flows of capital, information, goods and people, and they have international airports, universities, media and cultural institutions. They are not necessarily the largest by population: Zurich, Singapore and Hong Kong are influential for their size.

The Globalization and World Cities (GaWC) research network ranks cities by their connectivity through the offices of advanced producer services firms, and divides them into Alpha, Beta, Gamma and Sufficiency levels. London and New York have consistently been at the top (“Alpha++”), followed by cities such as Hong Kong, Singapore, Shanghai, Beijing, Dubai, Paris and Tokyo. Other rankings combine business activity, human capital, culture and political engagement. World cities also show social polarization, with a high-income professional class and a large low-paid workforce providing services.

What are megacities?

The UN defines a megacity as an urban agglomeration of at least 10 million people. In 1950, only New York and Tokyo had passed this level. By 1990 there were 10, and by 2018, 33, of which about two thirds were in the global South. Tokyo is the largest, with more than 37 million people in its metropolitan area, followed by cities such as Delhi, Shanghai, Dhaka, São Paulo, Cairo, Mexico City, Beijing, Mumbai and Osaka. The fastest growth is in Asia and Africa, with Lagos and Kinshasa expected to join the group or grow rapidly, while some cities in Japan and Europe are stable or declining. Not all large cities are megacities, and most of the world’s urban population actually lives in much smaller cities of fewer than 1 million inhabitants.

Megacities offer economies of scale, jobs, innovation and services, and they concentrate a large share of national output. They also face housing shortages and informal settlements, traffic and pollution, pressure on water and waste systems, vulnerability to hazards such as floods and earthquakes (Tokyo, Dhaka, Manila, Jakarta) and inequality. Many are coastal, so they are exposed to sea-level rise.

What are megalopolises?

The French geographer Jean Gottmann introduced the term in his 1961 book Megalopolis to describe the northeastern seaboard of the United States, where cities such as Boston, New York, Philadelphia, Baltimore and Washington had grown together by suburban sprawl and were linked by dense transport, finance and services into a single urban region of tens of millions of people. Other examples include the Tokaido corridor in Japan (Tokyo-Nagoya-Osaka), the Rhine-Ruhr and Randstad regions in Europe, the Pearl River Delta in China (Guangzhou, Shenzhen, Hong Kong), the Yangtze River Delta around Shanghai, and the São Paulo-Rio de Janeiro corridor. Terms such as conurbation (merging towns), megaregion and city region are also used. Planning problems of megalopolises include regional transport, governance across many administrations, preserving green space and sharing the costs and benefits.

What opportunities and challenges do they bring?

Big urban regions bring together people, firms and ideas, and these agglomeration economies raise productivity and innovation. They are also where the pressures of urbanization are most evident: affordable housing, mobility, energy and carbon emissions, waste, and risks from heat and floods. Governments respond with public transport (metros, rail), planning of new centers to relieve pressure on the core, investment in water and drainage, and climate adaptation. At the global scale, the networks of world cities are the places where decisions about finance, trade and technology are made, and which shape the position of other regions.

The concepts compared

Worked example: size, growth and share

1. Growth in the number of megacities: the number rose from 10 in 1990 to 33 in 2018. The increase is 23, or 23 ÷ 10 = 230%. Over 28 years, the average annual growth rate is (33 ÷ 10)^1/28 − 1 = 3.3^1/28 − 1 = 4.4% per year.
2. Share of urban population: if the 33 megacities have a combined population of about 530 million and the world’s urban population is about 4,200 million, they hold 530 ÷ 4,200 = 12.6% of it, which shows that most city dwellers live in smaller places.
3. City growth: a megacity of 15 million grows at 2.5% a year. In 10 years, it has 15 × 1.025¹⁰ = 15 × 1.28 = 19.2 million, an addition of 4.2 million. The doubling time is 70 ÷ 2.5 = 28 years.
4. Density: a megacity with 20 million people in an area of 2,500 km² has a density of 20,000,000 ÷ 2,500 = 8,000 people per km².
5. Megalopolis scale: a corridor of 600 km in length with a population of 50 million has an average of 50,000,000 ÷ 600 = about 83,000 people per km of corridor.
6. Economic share: a city with 8% of the national population produces 18% of the national output, so its output per person is 18 ÷ 8 = 2.25 times the national average.

How did the concepts develop?

Patrick Geddes coined the word “conurbation” in 1915, and the idea of a world city appeared in Geddes’s work as well, in the early 20th century. Peter Hall’s The World Cities (1966), Friedmann’s world city hypothesis (1986) and Sassen’s work (1991) developed the modern idea, supported by the globalization of finance in the 1980s. Gottmann’s megalopolis (1961) described the first huge urban region. The category of megacity grew from the UN’s classification in its World Urbanization Prospects, with a growing number of cities passing 10 million, especially in Asia since the 1980s. In recent years, researchers also emphasize the networks between cities, the role of secondary cities and the idea that city regions are the main units of economic competition.

Which mistakes are common?

Mistake 1: Using “megacity” and “world city” interchangeably

A megacity is defined by population. A world city is defined by its role in the global economy. Many megacities are not major global centers, and some influential world cities are small.

Mistake 2: Thinking that most urban people live in megacities

Only about one in eight urban dwellers lives in a megacity. Most live in cities of under 1 million.

Mistake 3: Confusing city proper and urban agglomeration

Population figures can vary widely depending on whether they refer to the city limits, the continuously built-up area or the wider metropolitan region.

Mistake 4: Treating a megalopolis as a single governed city

Megalopolises consist of many cities and administrations, with problems of coordination in planning and transport.