A megacity is defined by the United Nations as a city which has a population of 10 million or more people. Currently, there are 37 megacities in the world. These cities include Tokyo, New York, Paris, Berlin, and Bangkok among others. The 2017 UN statistics indicate that the cities with the largest populations worldwide are Tokyo and Shanghai with 38.8 million and 35.5 million people respectively.
A megacity is a very large city, typically with a population of more than 10 million people. Precise definitions vary: the United Nations Department of Economic and Social Affairs in its 2014 "World Urbanization Prospects" report counted urban agglomerations having over 10 million inhabitants. A University of Bonn report held that they are "usually defined as metropolitan areas with a total population of 10 million or more people". Others list cities satisfying criteria of either 5 or 8 million and also have a population density of 2,000 per square kilometre. The terms conurbation, metropolis, and metroplex are also applied to the latter.
Characteristics of megacities
On this page, we look at characteristics of megacities, including site, function, land use, their place in the hierarchy of settlement and growth processes.
Dhaka, Bangladesh: With a population of around 15-20 million people, Dhaka is an example of a megacity, defined as a city of 10 million people or more. Source: By the author.
What is a megacity?
A megacity is a city with a population of 10 million people or more. A metacity is a city with 20 million or more people.
Global distribution
In January 2015, China’s Pearl River Delta conurbation overtook Tokyo as the world’s largest city (Van Mead, 2016). However, this depends on how the ‘city’ is measured – the Pearl River Delta includes the cities of Shenzhen, Guangzhou, Foshan and Dongguan (but not Hong Kong, which is considered a separate territory under its ‘Special Administrative Zone’ status within China). If these cities were measured separately, Tokyo would likely remain the world’s largest city.
Most of the world’s megacities are found in Asia, as shown on the map below. They are also often found in coastal locations.
Global patterns of urbanisation, 2015. Source: UN Habitat, 2016, p8.
Characteristics of megacities
Megacities are often agglomerations, created when two or more towns and cities grow so large that they join together. This is slightly different from a conurbation which occurs when two cities become treated as a single urban area, but there may still be green space between them.
At the start of the 20th century, only London and New York could be considered megacities. At that time, just 2% of the world’s population lived in cities. The following years saw an increase in the number and a change in distribution, to now when over 50% of people live in cities producing 80% of the world’s economic output. Megacities are now growing faster in the developing world compared to the richest countries.
Due to their increasing size and the sheer number of people in them, megacities have specific problems such as water supply, waste management and the sustainability of the housing stock.
Site
The site of most megacities is the same as any other large city:
An adequate supply of fresh water, usually from a major river
Often coastal which makes it easy for trade, and therefore employment
A large area of flat land suitable for building
Land that is generally well drained, although the increase in the size of megacities in the second half of the 20th century has happened so recently that technological solutions have been found for poor drainage in some places
However, megacities have often not had the requirement to be good defensive sites as the world has been more peaceful in the modern era. Things like hilltops, river meanders and coastal cliffs are frequently not site factors for megacities. Similarly the site often doesn’t have the resources to support the population on site. For example, water supplies that were historically on site (fresh water springs, and rivers) are more likely to be piped from the surrounding rural areas.
Situation
As most megacities are coastal, their situation is generally conducive to trade, and this was the original situational feature that made the city grow in that location. However, recent megacity growth is due to a positive feedback loop between accessibility for migrants, and the development of transport infrastructure. As modern transport networks (especially highways and trains) have developed, they have made it easier for migrants to reach the megacity. The population increases, and with it the size of the economy. More money can be spent on developing transport links to the rest of the country, which then makes it even easier for migrants to reach the city.
The reason that cities grow is usually because of in-migration. People migrate to the city because of the economic and social opportunities there. These opportunities are better because of the situation of the city: it is well situated to take advantage of trade opportunities with other places. This is closely linked to the idea of regional economic growth, and in particular the concept of core-periphery development. John Friedmann’s Model of Regional Development (1966) and his related World City Hypothesis (1986) are both strongly linked to the development of large cities including megacities, and are covered elsewhere on this site.
Function
All cities have multiple functions, such as industrial, political, residential and commercial. Smaller cities can often be identified as having one main function that stands out more than others (such as Canberra in Australia which has a political function; Oxford in England has an educational function; Chongqing in China has a manufacturing function; Frankfurt has a financial function).
Megacities are so large that they usually have multiple functions and it is difficult to identify a single main function. They often have industrial and transport functions, but also act as hubs (centres) of commerce and finance, educational excellence, and as political and administrative headquarters.
Land use
The land use of megacities is usually highly varied. Megacities have almost always grown so large that they swallow up the surrounding settlements and result in a land use pattern that has distinct local centres within it, but may not have any obvious central business district. This fits closely with the Multiple Nuclei model of urban land use, developed by Ullman and Harris in 1945. Land use across the city varies in many ways, with no particular pattern, compared to smaller cities which often have clear sectors arranged in particular ways.
Models of urban land use. Source: Harris and Ullman, 1945.
Hierarchy of settlement
Megacities are towards the top of the settlement hierarchy, meaning they have a large population but there are very few of them. One example of a settlement hierarchy is shown below. A megacity is often also a ‘primate city’ (a city twice as big as the next biggest city in the country).
An example of a settlement hierarchy. Source: By the author.
Megacities are at the top of the hierarchy because of their population size (at least 10 million people), land area, variety of functions and their small number. However, other types of city may also appear at the top:
Metacity / hypercity / megalopolis – a city of at least 20 million people (UN Habitat, 2006). These terms are also used to describe large conurbations such as the Pearl River Delta area in southern China.
Conurbation – an urban area created when two or more large settlements grow so big that they join together.
Growth process (planned or spontaneous)
Urbanization is the term used to describe an increasing proportion of a population residing in urban areas. The difference between urban growth and urbanization is that urban growth reflects an increase in either the land area or the population size of an urban area. Urbanization is about the relative proportion of people residing in rural or urban areas in a given area (such as a region, country or continent).
Megacities tend to grow in both the land area and population, and also affect the proportion of people living in rural areas compared to urban areas. Both urban growth and urbanisation happen with many megacities.
The growth of megacities is generally unplanned, as the city grows due to large amounts of migration from rural areas. In Bangladesh, migration from rural areas to the capital Dhaka has swelled the city and it is one of the most densely populated cities on Earth. The city authorities have been unable to cope with the intense growth, leading to problems such as flooding, overcrowding, poor quality construction (and associated fires and building collapse) and the development of squatter settlements.
The main exception to this rule is China. As the map below shows, Chinese migration in the 1990s (and into the 2000s) was at a massive rate. This migration was planned by the central government in an effort to reduce poverty in China and provide workers for the huge industrial expansion that occurred in the period. The growth of Chinese megacities including Shanghai and the Pearl River Delta region was carefully planned and these cities have strong public transport networks, service provision and economic opportunities for the incoming migrants.
Internal migration in China from 1995 to 2000, with colour shading according to the Human Development Index. Source: UNDP, 2009 p11.
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