The total number of megacities in the world varies between different sources and their publication dates. The world had 33 according to UN DESA (in 2018), 25 according to the OCDE, 45 according to CityPopulation.de (in 2023), and 44 according to Demographia (in 2023). A good percentage of these urban agglomerations are in China and India. The other four countries with more than one megacity are Brazil, Japan, Pakistan, and the United States. African megacities are present in Nigeria, Egypt, South Africa, Angola and the DRC; European megacities are present in Russia, France, the United Kingdom, and Turkey (also in Asia); megacities can be found in Latin America in the countries of Brazil, Mexico, Colombia, Peru, and Argentina.
Since, presently, urban data are based on arbitrary definitions that vary from country to country and from year or census to the next, making them difficult to compare, an Urban Metric System (UMS) has been conceived that could correct the problem,[12] since it allows computing the urban area limits and central points, and it can be applied in the same way to all past, present and future population and job distributions.
It is based on vector field calculations obtained by assuming that, in a given space, all inhabitants and jobs exert the same attractive force A and repulsive force R. The net force (A - R) exerted by each inhabitant or job is given by [1/(1 + d)] - [1/( β + d/2)], where d = distance and β is the only parameter.
UMS distinguishes the following types of urban areas(including "patropolises" that are tantamount to "megacities"), each type corresponding to a given value of β:
Urban area
Distance at which the attractive force = the repulsive force
Value of β
1
Central city
10 km
6
2
Agglomeration
20 km
11
3
Metropolis
40 km
21
4
Patropolis
80 km
41
5
Megalopolis
160 km
81
6
Urban system
320 km
161
7
Urban macrosystem
640 km
321
8
Continental system
1,280 km
641
9
Intercontinental system
2,560 km
1,281
10
World system
5,120 km
2,561
UMS has been applied to some Canadian cases since 2018, but the data presented in this article are still based on the various existing national definitions, which are disparate.
The term "megacity" entered common use in the late 19th or early 20th centuries; one of the earliest documented uses of the term was by the University of Texas in 1904.[14] Initially the United Nations used the term to describe cities of 8 million or more inhabitants, but now uses the threshold of 10 million.[15] In the mid 1970s the term was coined by urbanist Janice Perlman referring to the phenomenon of very large urban agglomerations.[16]
Map showing urban areas with at least one million inhabitants in 2020
In 1800, only 3% of the world's population lived in cities, a figure that rose to 47% by the end of the twentieth century. In 1950, there were 83 cities with populations exceeding one million; by 2007, this number had risen to 468,[17] with 153 of them located in Asia. Among the 27 megacities with populations over 10 million globally, 15 were situated in Asia.[18]
In 2010, UN forecasted that urban population of 3.2 billion would rise to nearly 5 billion by 2030, when three out of five, or 60%, of people would live in cities.[19] This increase will be most dramatic on the least-urbanized continents, Asia and Africa. Surveys and projections indicate that all urban growth over the next 25 years will be in developing countries.[20] One billion people, almost one-seventh of the world's population, now live in shanty towns.[21] In many poor countries, overcrowded slums exhibit high rates of disease due to unsanitary conditions, malnutrition, and lack of basic health care.[22] By 2030, over 2 billion people in the world will be living in slums.[23] Over 90% of the urban population of Ethiopia, Malawi and Uganda, three of the world's most rural countries, already live in slums.
By 2025, Asia alone will have at least 30 megacities, including Mumbai, India (2015 population of 20.75 million people), Shanghai, China (2015 population of 35.5 million people), Delhi, India (2015 population of 21.8 million people), Tokyo, Japan (2015 population of 38.8 million people) and Seoul, South Korea (2015 population of 25.6 million people). The top eight provincial capital cities in China with urban areas exceeding 400 km²—Beijing, Shanghai, Tianjin, Guangzhou, Chongqing, Hangzhou, Wuhan, and Xi'an—accounted for 54.8% of the total urban area of all provincial capital cities in the country in 2015.[18]
In Africa, Lagos, Nigeria has grown from 300,000 in 1950 to an estimated 21 million today.
For almost five hundred years, during the period of the Republic and later of the Empire, Rome was the largest, wealthiest, and most politically important city of the ancient world, rulling over Europe, Western Asia and Northern Africa.[24][25] It is often stated that its population passed one million people by the end of the 1st century BC, however, its sometimes debated about whether the population actually reached such a large size.[26][27] Rome's population started declining in 402 AD when Flavius Honorius, Western Roman Emperor from 395 to 423, moved the government to Ravenna and Rome's population declined to a mere 20,000 during the Early Middle Ages, reducing the sprawling city to groups of inhabited buildings interspersed among large areas of ruins and vegetation.
Baghdad was likely the largest city in the world from shortly after its foundation in 762 AD until the 930s, with some estimates putting its population at over one million.[28] Chinese capital cities Chang'an and Kaifeng also experienced huge population booms during prosperous empires. According to the census in the year 742 recorded in the New Book of Tang, 362,921 families with 1,960,188 persons were counted in Jingzhao Fu (京兆府), the metropolitan area including small cities in the vicinity of Chang'an.[29] The medieval settlement surrounding Angkor, the one-time capital of the Khmer Empire which flourished between the 9th and 15th centuries, could have supported a population of up to one million people.[30]
During the 19th century, London was transformed into the world's largest city and capital of the British Empire.
From around 1825 to 1918 London was the largest city in the world, with the population growing rapidly; it was the first city to reach a population of over 5 million in 1900. In 1950, New York City was the only urban area with a population of over 10 million.[31] Geographers had identified 25 such areas as of October 2005,[32] as compared with 19 megacities in 2004 and only nine in 1985. This increase has happened as the world's population moves towards the high (75–85%) urbanization levels of North America and Western Europe.
Since the 2000s, the largest megacity has been the Greater Tokyo Area. The population of this urban agglomeration includes areas such as Yokohama and Kawasaki, and is estimated to be between 37 and 38 million. This variation in estimates can be accounted for by different definitions of what the area encompasses. While the prefectures of Tokyo, Chiba, Kanagawa, and Saitama are commonly included in statistical information, the Japan Statistics Bureau only includes the area within 50 kilometers of the Tokyo Metropolitan Government Offices in Shinjuku, thus arriving at a smaller population estimate.[33][34] A characteristic issue of megacities is the difficulty in defining their outer limits and accurately estimating the populations.
Another list defines megacities as urban agglomerations instead of metropolitan areas.[35] As of 2021, there are 28 megacities by this definition, like Tokyo.[36] Other sources list Nagoya[9] and the Rhein-Ruhr[37] as megacities.
Mumbai's Dharavi slum is home to 1 million residents
According to the United Nations, the proportion of urban dwellers living in slums or informal settlements decreased from 47 percent to 37 percent in the developing world between 1990 and 2005.[38] However, due to rising population, the absolute number of slum dwellers is rising. The majority of these are located in informal settlements which often lack sufficient quality housing, sanitation, drainage, water access, and officially recognized addresses. The increase in informal settlement population has been caused by massive migration, both internal and transnational, into cities, which has caused growth rates of urban populations and spatial concentrations not seen before in history.[citation needed] These issues raise problems in the political, social, and economic arenas.[citation needed] People who live in slums or informal settlements often have minimal or no access to education, healthcare, or the urban economy.
As with any large concentration of people, there is usually crime.[39][40] High population densities often result in higher crime rates, as visibly seen in growing megacities such as Karachi, Delhi, Cairo, Rio de Janeiro, and Lagos.[41]
Homelessness
Megacities often have significant numbers of homeless people. The actual legal definition of homelessness varies from country to country, or among different entities or institutions in the same country or region.[42]
In 2002, research showed that children and families were the largest growing segment of the homeless population in the United States,[43][44] and this has presented new challenges, especially in services, to agencies.
In the US, the government asked many major cities to come up with a ten-year plan to end homelessness. One of the results of this was a "Housing first" solution, rather than to have a homeless person remain in an emergency homeless shelter it was thought to be better to quickly get the person permanent housing of some sort and the necessary support services to sustain a new home. But there are many complications with this kind of program and these must be dealt with to make such an initiative work successfully in the middle to long term.[45][46]
Traffic congestion is a condition on road networks that occurs as use increases, and is characterized by slower speeds, longer trip times, increased pollution, and increased vehicular queueing. The Texas Transportation Institute estimated that, in 2000, the 75 largest metropolitan areas experienced 3.6 billion vehicle-hours of delay, resulting in 5.7 billion U.S. gallons (21.6 billion liters) in wasted fuel and $67.5 billion in lost productivity, or about 0.7% of the nation's GDP. It also estimated that the annual cost of congestion for each driver was approximately $1,000 in very large cities and $200 in small cities.[47] Traffic congestion is increasing in major cities and delays are becoming more frequent in smaller cities and rural areas. It also can result in various issues, including economic losses, energy waste, air and noise pollution, and more.[18]
Urban sprawl
A flat land area in the Greater Los Angeles Area in the U.S. state of California with houses, buildings, roads, and freeways. Areas constructed to capacity contribute to urban expansion.
Urban sprawl, also known as suburban sprawl, is a multifaceted concept, which includes the spreading outwards of a city and its suburbs to its outskirts to low-density, auto-dependent development on rural land, with associated design features that encourage car dependency.[48] As a result, some critics argue that sprawl has certain disadvantages including longer transport distances to work, high car dependence, inadequate facilities (e.g. health, cultural. etc.) and higher per-person infrastructure costs. Discussions and debates about sprawl are often obfuscated by the ambiguity associated with the phrase. For example, some commentators measure sprawl only with the average number of residential units per acre in a given area. But others associate it with decentralization (spread of population without a well-defined center), discontinuity (leapfrog development), segregation of uses, etc.[49]
Gentrification
Gentrification and urban gentrification are terms for the socio-cultural changes in an area as a result of wealthier people buying property in a less prosperous community.[50] As living costs rise, lower-income residents are forced to move out of the community leading to an increase in average income, which in turn makes the area more desirable to other wealthier property or business owners, further pushing the living costs up. This process also tends to lead to a decrease in average family size in the area. This type of population change reduces industrial land use when it is redeveloped for commerce and housing.
The sheer size and complexity of megacities gives rise to enormous social and environmental challenges. Whether megacities can develop sustainably depends to a large extent on how they obtain, share, and manage their energy and material resources. There are correlations between electricity consumption, heating and industrial fuel use, ground transportation energy use, water consumption, waste generation, and steel production in terms of level of consumption and how efficiently they use resources.[54]
A metropolitan area or metro is a region consisting of a densely populated urban agglomeration and its surrounding territories which share industries, commercial areas, transport network, infrastructures and housing. A metropolitan area usually comprises multiple principal cities, jurisdictions and municipalities: neighborhoods, townships, boroughs, cities, towns, exurbs, suburbs, counties, districts and even states and nations in areas like the eurodistricts. As social, economic and political institutions have changed, metropolitan areas have become key economic and political regions.
A conurbation is a region comprising a number of metropolises, cities, large towns, and other urban areas which, through population growth and physical expansion, have merged to form one continuous urban or industrially developed area. In most cases, a conurbation is a polycentric urbanised area in which transportation has developed to link areas. They create a single urban labour market or travel to work area.
The Greater Tokyo Area is the most populous metropolitan area in the world, consisting of the Kantō region of Japan as well as the prefecture of Yamanashi of the neighboring Chūbu region. In Japanese, it is referred to by various terms, one of the most common being Capital Region.
Urban sprawl is defined as "the spreading of urban developments on undeveloped land near a more or less densely populated city". Urban sprawl has been described as the unrestricted growth in many urban areas of housing, commercial development, and roads over large expanses of land, with little concern for very dense urban planning. Sometimes the urban areas described as the most "sprawling" are the most densely populated. In addition to describing a special form of urbanization, the term also relates to the social and environmental consequences associated with this development. In modern times some suburban areas described as "sprawl" have less detached housing and higher density than the nearby core city. Medieval suburbs suffered from the loss of protection of city walls, before the advent of industrial warfare. Modern disadvantages and costs include increased travel time, transport costs, pollution, and destruction of the countryside. The revenue for building and maintaining urban infrastructure in these areas are gained mostly through property and sales taxes. Most jobs in the US are now located in suburbs generating much of the revenue, although a lack of growth will require higher tax rates.
An urban area is a human settlement with a high population density and an infrastructure of built environment. This is the core of a metropolitan statistical area in the United States, if it contains a population of more than 50,000.
The Bangkok Metropolitan Region (BMR), may refer to a government-defined "political definition" of the urban region surrounding the metropolis of Bangkok, or the built-up area, i.e., urban agglomeration of Bangkok, Thailand, which varies in size and shape, and gets filled in as development expands.
A primate city is a city that is the largest in its country, province, state, or region, and disproportionately larger than any others in the urban hierarchy. A primate city distribution is a rank-size distribution that has one very large city with many much smaller cities and towns and no intermediate-sized urban centers, creating a statistical king effect.
A metropolis is a large city or conurbation which is a significant economic, political, and cultural area for a country or region, and an important hub for regional or international connections, commerce, and communications.
Earth has a human population of over 8 billion as of 2024, with an overall population density of 50 people per km2. Nearly 60% of the world's population lives in Asia, with more than 2.8 billion in the countries of India and China combined. The percentage shares of China, India and rest of South Asia of the world population have remained at similar levels for the last few thousand years of recorded history. The world's literacy rate has increased dramatically in the last 40 years, from 66.7% in 1979 to 86.3% today. Lower literacy levels are mostly attributable to poverty. Lower literacy rates are found mostly in South Asia and Sub-Saharan Africa.
A secondary city is an urban hub that fills specific regional and local needs related to governance, economics, finance, education, trade, transportation. A secondary city is defined by population, area, function, and economic status, but also by their relationship to neighboring and distant cities and their socio-economic status. A secondary city may emerge from a cluster of smaller cities in a metropolitan region or may be the capital city of a province, state, or second-tier administrative unit within a country. Secondary cities are the fastest-growing urban areas in lower- and middle-income countries, experiencing unplanned growth and development. By 2030, there will be twice as many medium-size cities as there were in 1990, outnumbering the total number of megacities. According to the World Bank, secondary cities make up almost 40% of the world cities population. Many secondary cities in the Global South are expected to undergo massive expansions in the next few decades comparable to city growth in Europe and North America over the past two centuries. These cities are unique environments that generally have limited data and information on infrastructure, land tenure, and planning.
Kollam Metropolitan Area is the 4th largest Metropolis in Kerala and 14th largest urban agglomeration in South India. It is one of the 10 fastest growing cities in the world covering an area of 364.51 km2 (2015) with a 31.1% urban growth between 2015 and 2020 as per the survey conducted by Economist Intelligence Unit (EIU) based on urban area growth during January 2020.
The Abidjan–Lagos Corridor, also known as the Abidjan–Lagos Megalopolis, is an emerging transnational megalopolis on the coast of southern West Africa. It stretches from Abidjan to Lagos, crossing five independent states from west to east, and includes two political capitals and many regional economic centers. The corridor has a length of approximately 965 kilometers. Within the megalopolis, a significant portion of West Africa's economic output is generated, and cities within the corridor are among the most economically developed of their respective countries, for which agglomeration effects and access to the Atlantic Ocean are responsible. The population within the region is experiencing rapid growth, and nearly 50 million people are expected to live within the corridor by 2035. According to projections, by the end of the 21st century, the region could become the largest urban region with continuous settlement in the world, then with up to half a billion inhabitants.
↑ Tertius Chandler, 1987, St. David's University Press. "Top 10 Cities of the Year 1950". Four Thousand Years of Urban Growth: An Historical Census. Archived from the original on 2016-04-15. Retrieved 2007-03-24.{{cite web}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)
↑ National Coalition for the Homeless, "Homeless Youth" 2005 "Homeless Youth"(PDF). Archived from the original(PDF) on 2018-08-22. Retrieved 2013-04-15.(164KB)
↑ Namu, Adilifu (2008). Black space: imagining race in science fiction film. University of Texas Press. ISBN978-0-292-71745-9.
↑ Westfahl, Gary (2005). The Greenwood encyclopedia of science fiction and fantasy: themes, works, and wonders, Volume 2. Greenwood Publishing Group. ISBN978-0-313-32952-4.
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