Megacity - AbsoluteAstronomy.com

A megacity is usually defined as a metropolitan area

Metropolitan area

The term metropolitan area refers to a region consisting of a densely populated urban core and its less-populated surrounding territories, sharing industry, infrastructure, and housing. A metropolitan area usually encompasses multiple jurisdictions and municipalities: neighborhoods, townships,...

with a total population

Population

A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...

in excess of 10 million people. Some definitions also set a minimum level for population density

Population density

Population density is a measurement of population per unit area or unit volume. It is frequently applied to living organisms, and particularly to humans...

(at least 2,000 persons/square km). A megacity can be a single metropolitan area

Metropolitan area

or two or more metropolitan areas that converge. The terms conurbation

Conurbation

A conurbation is a region comprising a number of cities, large towns, and other urban areas that, through population growth and physical expansion, have merged to form one continuous urban and industrially developed area...

, metropolis

Metropolis

A metropolis is a very large city or urban area which is a significant economic, political and cultural center for a country or region, and an important hub for regional or international connections and communications...

and metroplex are also applied to the latter. The terms "megapolis'" and megalopolis

Megalopolis (term)

A megalopolis is typically defined as a chain of roughly adjacent metropolitan areas. The term was used by Oswald Spengler in his 1918 book, The Decline of the West, and Lewis Mumford in his 1938 book, The Culture of Cities, which described it as the first stage in urban overdevelopment and...

are sometimes used synonymously with megacity," though those terms denote a semi-continuous chain of large metropolitan cities.

As of 2011, there are 21 megacities in existence, which is the official figure despite the list below containing 27 megacities – with conurbations such as Mumbai

Mumbai

Mumbai , formerly known as Bombay in English, is the capital of the Indian state of Maharashtra. It is the most populous city in India, and the fourth most populous city in the world, with a total metropolitan area population of approximately 20.5 million...

, Tokyo

Tokyo

, ; officially , is one of the 47 prefectures of Japan. Tokyo is the capital of Japan, the center of the Greater Tokyo Area, and the largest metropolitan area of Japan. It is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family...

, Seoul

Seoul

Seoul , officially the Seoul Special City, is the capital and largest metropolis of South Korea. A megacity with a population of over 10 million, it is the largest city proper in the OECD developed world...

, New York City

New York City

New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...

, Dhaka

Dhaka

Dhaka is the capital of Bangladesh and the principal city of Dhaka Division. Dhaka is a megacity and one of the major cities of South Asia. Located on the banks of the Buriganga River, Dhaka, along with its metropolitan area, had a population of over 15 million in 2010, making it the largest city...

, and Mexico City

Mexico City

Mexico City is the Federal District , capital of Mexico and seat of the federal powers of the Mexican Union. It is a federal entity within Mexico which is not part of any one of the 31 Mexican states but belongs to the federation as a whole...

having populations in excess of 20 million inhabitants each. New Megacities like Johannesburg have population of over 10 million.

History

In 1800, only 3% of the world's population

World population

The world population is the total number of living humans on the planet Earth. As of today, it is estimated to be billion by the United States Census Bureau...

population lived in cities, a figure that has risen 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. If the trend continues, the world's urban population

Metropolis

will double every 38 years. The UN forecasts that today's urban population of 3.2 billion will rise to nearly 5 billion by 2030, when three out of five people will live in cities.

This increase will be most dramatic on the least-urbanized continents, Asia

Asia

Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

and Africa

Africa

Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

. Surveys and projections indicate that all urban growth over the next 25 years will be in developing countries. One billion people, almost one-seventh of the world's population, now live in shanty towns. In many poor countries overpopulated

Overpopulation

Overpopulation is a condition where an organism's numbers exceed the carrying capacity of its habitat. The term often refers to the relationship between the human population and its environment, the Earth...

slums exhibit high rates of disease due to unsanitary conditions, malnutrition, and lack of basic health care. By 2030, over 2 billion people in the world will be living in slums. Over 90% of the urban population of Ethiopia

Ethiopia

Ethiopia , officially known as the Federal Democratic Republic of Ethiopia, is a country located in the Horn of Africa. It is the second-most populous nation in Africa, with over 82 million inhabitants, and the tenth-largest by area, occupying 1,100,000 km2...

, Malawi

Malawi

The Republic of Malawi is a landlocked country in southeast Africa that was formerly known as Nyasaland. It is bordered by Zambia to the northwest, Tanzania to the northeast, and Mozambique on the east, south and west. The country is separated from Tanzania and Mozambique by Lake Malawi. Its size...

and Uganda

Uganda

Uganda , officially the Republic of Uganda, is a landlocked country in East Africa. Uganda is also known as the "Pearl of Africa". It is bordered on the east by Kenya, on the north by South Sudan, on the west by the Democratic Republic of the Congo, on the southwest by Rwanda, and on the south by...

, three of the world's most rural countries, already live in slums.

By 2025, according to the Far Eastern Economic Review, Asia alone will have at least 10 megacities, including Mumbai

Mumbai

, India

India

India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

(33 million), Shanghai

Shanghai

Shanghai is the largest city by population in China and the largest city proper in the world. It is one of the four province-level municipalities in the People's Republic of China, with a total population of over 23 million as of 2010...

, China

China

Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

(27 million), Karachi, Pakistan

Karachi

Karachi is the largest city, main seaport and the main financial centre of Pakistan, as well as the capital of the province of Sindh. The city has an estimated population of 13 to 15 million, while the total metropolitan area has a population of over 18 million...

(26.5 million), Dhaka, Bangladesh

Dhaka

(26 million) and Jakarta, Indonesia

Jakarta

Jakarta is the capital and largest city of Indonesia. Officially known as the Special Capital Territory of Jakarta, it is located on the northwest coast of Java, has an area of , and a population of 9,580,000. Jakarta is the country's economic, cultural and political centre...

(24.9 million people). Lagos, Nigeria

Lagos

Lagos is a port and the most populous conurbation in Nigeria. With a population of 7,937,932, it is currently the third most populous city in Africa after Cairo and Kinshasa, and currently estimated to be the second fastest growing city in Africa...

has grown from 300,000 in 1950 to an estimated 12.5 million today, and the Nigerian government estimates that the city will have expanded to 25 million residents by 2015.

Growth

For almost a thousand years, Rome

Rome

Rome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in . The city is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.Rome's history spans two and a half...

was the largest, wealthiest, and most politically important city in Europe. Its population passed a million people by the end of the 1st century BC. Rome's population started dropping in 402 AD when Flavius Honorius

Honorius (emperor)

Honorius , was Western Roman Emperor from 395 to 423. He was the younger son of emperor Theodosius I and his first wife Aelia Flaccilla, and brother of the eastern emperor Arcadius....

moved the government to Ravenna

Ravenna

Ravenna is the capital city of the Province of Ravenna in the Emilia-Romagna region of Italy and the second largest comune in Italy by land area, although, at , it is little more than half the size of the largest comune, Rome...

and Rome's population declined to a mere 20,000 during the Early Middle Ages

Early Middle Ages

The Early Middle Ages was the period of European history lasting from the 5th century to approximately 1000. The Early Middle Ages followed the decline of the Western Roman Empire and preceded the High Middle Ages...

, reducing the sprawling city to groups of inhabited buildings interspersed among large areas of ruins and vegetation.

Baghdad

Baghdad

Baghdad is the capital of Iraq, as well as the coterminous Baghdad Governorate. The population of Baghdad in 2011 is approximately 7,216,040...

was likely the largest city in the world

Historical urban community sizes

Estimated populations of historical cities over time.-Neolithic settlements:-Bronze Age:-Iron Age:-Middle Ages:-Early Modern era:-20th century:-See also:*World population*Urbanism*List of metropolitan areas by population...

from shortly after its foundation in 762 AD until the 930s, with some estimates putting its population at over one million.

Chinese capital cities Chang'an

Chang'an

Chang'an is an ancient capital of more than ten dynasties in Chinese history, today known as Xi'an. Chang'an literally means "Perpetual Peace" in Classical Chinese. During the short-lived Xin Dynasty, the city was renamed "Constant Peace" ; yet after its fall in AD 23, the old name was restored...

, Kaifeng

Kaifeng

Kaifeng , known previously by several names , is a prefecture-level city in east-central Henan province, Central China. Nearly 5 million people live in the metropolitan area...

also experienced huge population booms during prosperous empires. According to the census in the year 742 recorded in the New Book of Tang

New Book of Tang

The New Book of Tang , is a classic work of history about the Tang Dynasty edited by Ouyang Xiu and Song Qi and other official scholars of the Song Dynasty. The emperor called for a revision of the former Book of Tang in 1044. The New Book was presented to the throne in 1060. It was given its...

, 362,921 families with 1,960,188 persons were counted in Jingzhao Fu (京兆府), the metropolitan area

Metropolitan area

including small cities in the vicinity.

The medieval settlement surrounding Angkor

Angkor

Angkor is a region of Cambodia that served as the seat of the Khmer Empire, which flourished from approximately the 9th to 15th centuries. The word Angkor is derived from the Sanskrit nagara , meaning "city"...

, the one-time capital of the Khmer Empire

Khmer Empire

The Khmer Empire was one of the most powerful empires in Southeast Asia. The empire, which grew out of the former kingdom of Chenla, at times ruled over and/or vassalized parts of modern-day Laos, Thailand, Vietnam, Burma, and Malaysia. Its greatest legacy is Angkor, the site of the capital city...

which flourished between the 9th and 15th centuries, could have supported a population of up to one million people.

In 1950, New York City

New York City

was the only urban area with a population of over 10 million. Geographers had identified 25 such areas as of October 2005, 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

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

and Western Europe

Western Europe

Western Europe is a loose term for the collection of countries in the western most region of the European continents, though this definition is context-dependent and carries cultural and political connotations. One definition describes Western Europe as a geographic entity—the region lying in the...

. The 1990 census marked the first time the majority of US citizens lived in cities with over 1 million inhabitants.

In the 2000s, the largest megacity is the Greater Tokyo Area

Greater Tokyo Area

The Greater Tokyo Area is a large metropolitan area in Kantō region, Japan, consisting of most of the prefectures of Chiba, Kanagawa, Saitama, and Tokyo . In Japanese, it is referred to by various terms, including the , , and others....

. The population of this urban agglomeration includes areas such as Yokohama

Yokohama

is the capital city of Kanagawa Prefecture and the second largest city in Japan by population after Tokyo and most populous municipality of Japan. It lies on Tokyo Bay, south of Tokyo, in the Kantō region of the main island of Honshu...

and Kawasaki

Kawasaki, Kanagawa

is a city located in Kanagawa Prefecture, Japan, between Tokyo and Yokohama. It is the 9th most populated city in Japan and one of the main cities forming the Greater Tokyo Area and Keihin Industrial Area....

, and is estimated to be between 35 and 36 million. This variation in estimates can be accounted for by different definitions of what the area encompasses. While the prefectures of Tokyo

Tokyo

, Chiba

Chiba Prefecture

is a prefecture of Japan located in the Kantō region and the Greater Tokyo Area. Its capital is Chiba City.- History :Chiba Prefecture was established on June 15, 1873 with the merger of Kisarazu Prefecture and Inba Prefecture...

, Kanagawa

Kanagawa Prefecture

is a prefecture located in the southern Kantō region of Japan. The capital is Yokohama. Kanagawa is part of the Greater Tokyo Area.-History:The prefecture has some archaeological sites going back to the Jōmon period...

, and Saitama

Saitama Prefecture

is a prefecture of Japan located in the Kantō region of the island of Honshu. The capital is the city of Saitama.This prefecture is part of the Greater Tokyo Area, and most of Saitama's cities can be described as suburbs of Tokyo, to which a large amount of residents commute each day.- History...

are commonly included in statistical information, the Japan Statistics Bureau only includes the area within 50 kilometers of the Tokyo Metropolitan Government Offices

Tokyo Metropolitan Government Building

The , also referred to as Tokyo City Hall or Tochō for short, houses the headquarters of the Tokyo Metropolitan Government, which governs not only the 23 wards, but also the cities, towns and villages that make up Tokyo as a whole....

in Shinjuku

Shinjuku, Tokyo

is one of the 23 special wards of Tokyo, Japan. It is a major commercial and administrative center, housing the busiest train station in the world and the Tokyo Metropolitan Government Building, the administration center for the government of Tokyo.As of 2008, the ward has an estimated population...

, thus arriving at a smaller population estimate. A characteristic issue of megacities is the difficulty in defining their outer limits and accurately estimating the populations.

Based on the population criteria, the world's 27 megacities are, in rank of population:

Rank	Megacity	Country	Continent	Population
1	Tokyo	Japan Japan Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...	Asia Asia Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...	34,300,000	0.60%
2	Guangzhou Guangzhou Guangzhou , known historically as Canton or Kwangchow, is the capital and largest city of the Guangdong province in the People's Republic of China. Located in southern China on the Pearl River, about north-northwest of Hong Kong, Guangzhou is a key national transportation hub and trading port...	China China Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...	Asia Asia Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...	25,200,000	4.00%
3	Seoul Seoul National Capital Area The Seoul National Capital Area is a region located in the north-west of South Korea. It is generally referred to as Sudogwon in Korean, and contains three different administrative districts; Seoul, Incheon and Gyeonggi-do....	South Korea South Korea The Republic of Korea , , is a sovereign state in East Asia, located on the southern portion of the Korean Peninsula. It is neighbored by the People's Republic of China to the west, Japan to the east, North Korea to the north, and the East China Sea and Republic of China to the south...	Asia Asia Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...	25,100,000	1.40%
4	Shanghai Shanghai Shanghai is the largest city by population in China and the largest city proper in the world. It is one of the four province-level municipalities in the People's Republic of China, with a total population of over 23 million as of 2010...	China China Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...	Asia Asia Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...	24,800,000	2.20%
5	Delhi National Capital Region (India) The National Capital Region in India is a name for the conurbation or metropolitan area which encompasses the entire National Capital Territory of Delhi as well as urban areas ringing it in neighbouring states of Haryana, Uttarakhand, Uttar Pradesh and Rajasthan...	India India India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...	Asia Asia Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...	23,300,000	4.60%
6	Mumbai Mumbai metropolitan area The Mumbai Metropolitan Region /Mumbai Metropolitan Area is the metropolitan area consisting of the metropolis of Mumbai and its satellite towns. Developing over a period of about 20 years, it consists of seven municipal corporations and fifteen smaller municipal councils...	India India India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...	Asia Asia Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...	23,000,000	2.90%
7	Mexico City Greater Mexico City Greater Mexico City refers to the conurbation around Mexico City, officially called Mexico City Metropolitan Area , constituted by the Federal District—itself composed of 16 boroughs—and 41 adjacent municipalities of the states of Mexico and Hidalgo...	Mexico Mexico The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...	North America North America North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...	22,900,000	2.00%
8	New York City New York metropolitan area The New York metropolitan area, also known as Greater New York, or the Tri-State area, is the region that composes of New York City and the surrounding region...	USA United States The United States of America is a federal constitutional republic comprising fifty states and a federal district...	North America North America North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...	22,000,000	0.30%
9	São Paulo Greater São Paulo The Greater São Paulo is a nonspecific term for one of the multiple definitions the large metropolitan area located in the São Paulo state in Brazil.-Definitions:-Metropolitan Area:...	Brazil Brazil Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...	South America South America South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...	20,900,000	1.40%
10	Manila Metro Manila Metropolitan Manila , the National Capital Region , or simply Metro Manila, is the metropolitan region encompassing the City of Manila and its surrounding areas in the Philippines...	Philippines Philippines The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...	Asia Asia Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...	20,300,000	2.50%
11	Jakarta Jakarta Jakarta is the capital and largest city of Indonesia. Officially known as the Special Capital Territory of Jakarta, it is located on the northwest coast of Java, has an area of , and a population of 9,580,000. Jakarta is the country's economic, cultural and political centre...	Indonesia Indonesia Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...	Asia Asia Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...	18,900,000	2.00%
12	Los Angeles Greater Los Angeles Area The Greater Los Angeles Area, or the Southland, is a term used for the Combined Statistical Area sprawled over five counties in the southern part of California, namely Los Angeles County, Orange County, San Bernardino County, Riverside County and Ventura County...	USA United States The United States of America is a federal constitutional republic comprising fifty states and a federal district...	North America North America North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...	18,100,000	1.10%
13	Karachi Karachi Karachi is the largest city, main seaport and the main financial centre of Pakistan, as well as the capital of the province of Sindh. The city has an estimated population of 13 to 15 million, while the total metropolitan area has a population of over 18 million...	Pakistan Pakistan Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...	Asia Asia Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...	17,000,000	4.90%
14	Osaka Osaka is a city in the Kansai region of Japan's main island of Honshu, a designated city under the Local Autonomy Law, the capital city of Osaka Prefecture and also the biggest part of Keihanshin area, which is represented by three major cities of Japan, Kyoto, Osaka and Kobe...	Japan Japan Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...	Asia Asia Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...	16,700,000	0.15%
15	Kolkata Kolkata Kolkata , formerly known as Calcutta, is the capital of the Indian state of West Bengal. Located on the east bank of the Hooghly River, it was the commercial capital of East India...	India India India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...	Asia Asia Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...	16,600,000	2.00%
16	Cairo Cairo Cairo , is the capital of Egypt and the largest city in the Arab world and Africa, and the 16th largest metropolitan area in the world. Nicknamed "The City of a Thousand Minarets" for its preponderance of Islamic architecture, Cairo has long been a centre of the region's political and cultural life...	Egypt Egypt Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...	Africa Africa Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...	15,300,000	2.60%
17	Buenos Aires Buenos Aires Buenos Aires is the capital and largest city of Argentina, and the second-largest metropolitan area in South America, after São Paulo. It is located on the western shore of the estuary of the Río de la Plata, on the southeastern coast of the South American continent...	Argentina Argentina Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...	South America South America South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...	14,800,000	1.00%
18	Moscow Moscow Moscow is the capital, the most populous city, and the most populous federal subject of Russia. The city is a major political, economic, cultural, scientific, religious, financial, educational, and transportation centre of Russia and the continent...	Russia Russia Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...	Europe Europe Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...	14,800,000	0.20%
19	Dhaka Dhaka Dhaka is the capital of Bangladesh and the principal city of Dhaka Division. Dhaka is a megacity and one of the major cities of South Asia. Located on the banks of the Buriganga River, Dhaka, along with its metropolitan area, had a population of over 15 million in 2010, making it the largest city...	Bangladesh Bangladesh Bangladesh , officially the People's Republic of Bangladesh is a sovereign state located in South Asia. It is bordered by India on all sides except for a small border with Burma to the far southeast and by the Bay of Bengal to the south...	Asia Asia Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...	14,000,000	4.10%
20	Beijing Beijing Beijing , also known as Peking , is the capital of the People's Republic of China and one of the most populous cities in the world, with a population of 19,612,368 as of 2010. The city is the country's political, cultural, and educational center, and home to the headquarters for most of China's...	China China Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...	Asia Asia Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...	13,900,000	2.70%
21	Tehran Tehran Tehran , sometimes spelled Teheran, is the capital of Iran and Tehran Province. With an estimated population of 8,429,807; it is also Iran's largest urban area and city, one of the largest cities in Western Asia, and is the world's 19th largest city.In the 20th century, Tehran was subject to...	Iran Iran Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...	Asia Asia Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...	13,100,000	2.60%
22	Istanbul Istanbul Istanbul , historically known as Byzantium and Constantinople , is the largest city of Turkey. Istanbul metropolitan province had 13.26 million people living in it as of December, 2010, which is 18% of Turkey's population and the 3rd largest metropolitan area in Europe after London and...	Turkey Turkey Turkey , known officially as the Republic of Turkey , is a Eurasian country located in Western Asia and in East Thrace in Southeastern Europe...	Europe Europe Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting... & Asia Asia Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...	13,000,000	2.80%
23	London London London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...	United Kingdom United Kingdom The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...	Europe Europe Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...	12,500,000	0.70%
24	Rio de Janeiro Rio de Janeiro Rio de Janeiro , commonly referred to simply as Rio, is the capital city of the State of Rio de Janeiro, the second largest city of Brazil, and the third largest metropolitan area and agglomeration in South America, boasting approximately 6.3 million people within the city proper, making it the 6th...	Brazil Brazil Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...	South America South America South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...	12,500,000	1.00%
25	Lagos Lagos Lagos is a port and the most populous conurbation in Nigeria. With a population of 7,937,932, it is currently the third most populous city in Africa after Cairo and Kinshasa, and currently estimated to be the second fastest growing city in Africa...	Nigeria Nigeria Nigeria , officially the Federal Republic of Nigeria, is a federal constitutional republic comprising 36 states and its Federal Capital Territory, Abuja. The country is located in West Africa and shares land borders with the Republic of Benin in the west, Chad and Cameroon in the east, and Niger in...	Africa Africa Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...	12,100,000	3.20%
26	Paris	France France The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...	Europe Europe Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...	10,197,678	1.00%

Source: Th. Brinkhoff: The Principal Agglomerations of the World, 2011-07-01

Another list defines megacities as urban agglomerations instead of metropolitan areas. As of 2010, there are 25 megacities by this definition.

Challenges

Slums

According to the United Nations, the proportion of urban dwellers living in slum

Slum

A slum, as defined by United Nations agency UN-HABITAT, is a run-down area of a city characterized by substandard housing and squalor and lacking in tenure security. According to the United Nations, the percentage of urban dwellers living in slums decreased from 47 percent to 37 percent in the...

s decreased from 47 percent to 37 percent in the developing world between 1990 and 2005. However, due to rising population, the absolute number of slum dwellers is rising. The majority of these come from the fringes of urban margins, located in legal and illegal settlements with insufficient housing and sanitation. This 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. These issues raise problems in the political, social, and economic arenas. Slum dwellers often have minimal or no access to education, healthcare, or the urban economy.

Homelessness

Megacities often have significant numbers of homeless

Homelessness

Homelessness describes the condition of people without a regular dwelling. People who are homeless are unable or unwilling to acquire and maintain regular, safe, and adequate housing, or lack "fixed, regular, and adequate night-time residence." The legal definition of "homeless" varies from country...

people. The actual legal definition of homelessness varies from country to country, or among different entities or institutions in the same country or region.

Traffic congestion

Traffic congestion is a condition on road networks that occurs as use increases, and is characterized by slower speeds, longer trip times, and increased vehicular queueing. The most common example is the physical use of roads by vehicles. When traffic demand is great enough that the interaction...

is a condition on road networks that occurs as use increases, and is characterized by slower speeds, longer trip times, and increased vehicular queueing

Queueing theory

Queueing theory is the mathematical study of waiting lines, or queues. The theory enables mathematical analysis of several related processes, including arriving at the queue, waiting in the queue , and being served at the front of the queue...

Urban sprawl

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 and auto-dependent development on rural land, high segregation of uses Urban sprawl, also known as suburban sprawl, is a...

, also known as suburban sprawl, is a multifaceted concept, which includes the spreading outwards of a city and its suburb

Suburb

The word suburb mostly refers to a residential area, either existing as part of a city or as a separate residential community within commuting distance of a city . Some suburbs have a degree of administrative autonomy, and most have lower population density than inner city neighborhoods...

s to its outskirts to low-density, auto-dependent development on rural land, with associated design features that encourage car dependency. 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.

Gentrification

Gentrification and urban gentrification refer to the changes that result when wealthier people acquire or rent property in low income and working class communities. Urban gentrification is associated with movement. Consequent to gentrification, the average income increases and average family size...

and urban gentrification denote the socio-cultural changes in an area resulting from wealthier people buying housing property in a less prosperous community. Consequent to gentrification, the average income increases and average family size decreases in the community, which may result in the informal economic eviction of the lower-income residents, because of increased rents, house prices, and property taxes. This type of population change reduces industrial land use

Land use

Land use is the human use of land. Land use involves the management and modification of natural environment or wilderness into built environment such as fields, pastures, and settlements. It has also been defined as "the arrangements, activities and inputs people undertake in a certain land cover...

when it is redeveloped for commerce and housing. In addition, new businesses, catering to a more affluent base of consumers, tend to move into formerly blighted areas, further increasing the appeal to more affluent migrants and decreasing the accessibility to less wealthy natives.

Air pollution

Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment, into the atmosphere....

is the introduction of chemicals, particulate matter, or biological material

Biological material

Biological material may refer to:* Tissue , or just tissue* Biomass, living or dead biological matter, often plants grown as fuel* Biomass , the total mass of living biological matter* Biomaterials...

s that cause harm or discomfort to humans or other living organisms, or damages the natural environment

Natural environment

The natural environment encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species....

, into the atmosphere

Earth's atmosphere

The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

. Many urban areas have significant problems with smog

Smog

Smog is a type of air pollution; the word "smog" is a portmanteau of smoke and fog. Modern smog is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine...

, a type of air pollution

Air pollution

derived from vehicular emission from internal combustion engine

Internal combustion engine

The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

s and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine with the primary emissions to form photochemical smog.

Smog is also caused by large amounts of coal

Coal

Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

burning, which creates a mixture of smoke and sulfur dioxide

Sulfur dioxide

Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...

. World coal consumption was about 6,743,786,000 short ton

Short ton

The short ton is a unit of mass equal to . In the United States it is often called simply ton without distinguishing it from the metric ton or the long ton ; rather, the other two are specifically noted. There are, however, some U.S...

s in 2006 and is expected to increase 48% to 9.98 billion short tons by 2030. China

Coal power in China

The People's Republic of China is the largest consumer of coal in the world, and is about to become the largest user of coal-derived electricity, generating 1.95 trillion kilowatt-hours per year, or 68.7% of its electricity from coal as of 2006...

produced 2.38 billion tons in 2006. India

India

produced about 447.3 million tons in 2006. 68.7%

Coal power in China

of China's electricity comes from coal. The USA consumes about 14% of the world total, using 90% of it for generation of electricity.

In fiction

Many of the following fictional cities were inspired by Fritz Lang
Fritz Lang
Friedrich Christian Anton "Fritz" Lang was an Austrian-American filmmaker, screenwriter, and occasional film producer and actor. One of the best known émigrés from Germany's school of Expressionism, he was dubbed the "Master of Darkness" by the British Film Institute...

's 1927 film, Metropolis and the influential depiction of Los Angeles
Los Ángeles
Los Ángeles is the capital of the province of Biobío, in the commune of the same name, in Region VIII , in the center-south of Chile. It is located between the Laja and Biobío rivers. The population is 123,445 inhabitants...

in Ridley Scott
Ridley Scott
Sir Ridley Scott is an English film director and producer. His most famous films include The Duellists , Alien , Blade Runner , Legend , Thelma & Louise , G. I...

's 1982 film, Blade Runner
Blade Runner
Blade Runner is a 1982 American science fiction film directed by Ridley Scott and starring Harrison Ford, Rutger Hauer, and Sean Young. The screenplay, written by Hampton Fancher and David Peoples, is loosely based on the novel Do Androids Dream of Electric Sheep? by Philip K...

.
Megacities are a common backdrop in dystopia
Dystopia
A dystopia is the idea of a society in a repressive and controlled state, often under the guise of being utopian, as characterized in books like Brave New World and Nineteen Eighty-Four...

n science fiction
Science fiction
Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...

, with examples such as the Sprawl
The Sprawl
In William Gibson's fiction, the Sprawl is a colloquial name for the Boston-Atlanta Metropolitan Axis , an urban sprawl environment on a massive scale, and a fictional extension of the real Northeast Megalopolis....

in William Gibson's Neuromancer, and Mega-City One
Mega-City One
Mega-City One is a huge fictional city-state covering much of what is now the Eastern United States in the Judge Dredd comic book series. The exact boundaries of the city depend on which artist has drawn the story...

, a megalopolis of over 400 million people across the east coast of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, in the Judge Dredd
Judge Dredd
Judge Joseph Dredd is a comics character whose strip in the British science fiction anthology 2000 AD is the magazine's longest running . Dredd is an American law enforcement officer in a violent city of the future where uniformed Judges combine the powers of police, judge, jury and executioner...

comic. In Demolition Man
Demolition Man (film)
Demolition Man is a 1993 American, science fiction action film directed by Marco Brambilla, and starring Sylvester Stallone and Wesley Snipes. Sandra Bullock, Nigel Hawthorne, and Denis Leary co-star....

a megacity called "San Angeles
San Angeles
San Angeles is a fictional futuristic concept of Southern California, United States, typically configured by commentators and films producers to include the areas of Los Angeles to San Diego and sometimes even San Bernardino to Riverside...

" was formed from the joining of Los Angeles
Los Ángeles
Los Ángeles is the capital of the province of Biobío, in the commune of the same name, in Region VIII , in the center-south of Chile. It is located between the Laja and Biobío rivers. The population is 123,445 inhabitants...

, Santa Barbara
Santa Barbara, California
Santa Barbara is the county seat of Santa Barbara County, California, United States. Situated on an east-west trending section of coastline, the longest such section on the West Coast of the United States, the city lies between the steeply-rising Santa Ynez Mountains and the Pacific Ocean...

, San Diego and the surrounding metropolitan regions following a massive earthquake in 2010.
Fictional planet-wide megacities (ecumenopoleis) include Trantor
Trantor
Trantor is a fictional planet in Isaac Asimov's Foundation Series and Empire Series of science fiction novels.Trantor was first described in a short story by Asimov appearing in Early Asimov Volume 1. Later Trantor gained prominence when the 1940s Foundation Series first appeared in print . Asimov...

in Isaac Asimov
Isaac Asimov
Isaac Asimov was an American author and professor of biochemistry at Boston University, best known for his works of science fiction and for his popular science books. Asimov was one of the most prolific writers of all time, having written or edited more than 500 books and an estimated 90,000...

's Foundation series of books and Coruscant
Coruscant
Coruscant is a planet in the fictional Star Wars universe. It first appeared onscreen in the 1997 Special Edition of Star Wars Episode VI: Return of the Jedi, but was first mentioned in Timothy Zahn's 1991 novel Heir to the Empire...

in the Star Wars
Star Wars
Star Wars is an American epic space opera film series created by George Lucas. The first film in the series was originally released on May 25, 1977, under the title Star Wars, by 20th Century Fox, and became a worldwide pop culture phenomenon, followed by two sequels, released at three-year...

universe. Other examples are 'City Europe' in David Wingrove
David Wingrove
David Wingrove is a British science fiction writer. He is well-known as the author of the Chung Kuo novels . He is also the co-author of the three Myst novels....

's Chung Kuo series of books, Holy Terra and the hive cities of Necromunda
Necromunda
Necromunda is a skirmish tabletop war game produced by Specialist Games .In Necromunda, players control rival gangs battling each other in the Underhive, a place of anarchy and violence in the depths below the Hive City...

in Warhammer 40,000
Warhammer 40,000
Warhammer 40,000 is a tabletop miniature wargame produced by Games Workshop, set in a dystopian science fantasy universe. Warhammer 40,000 was created by Rick Priestley in 1987 as the futuristic companion to Warhammer Fantasy Battle, sharing many game mechanics...

and Ravnica in the eponymous Magic: The Gathering
Magic: The Gathering
Magic: The Gathering , also known as Magic, is the first collectible trading card game created by mathematics professor Richard Garfield and introduced in 1993 by Wizards of the Coast. Magic continues to thrive, with approximately twelve million players as of 2011...

expansion.
The futuristic comic seriesTransmetropolitan
Transmetropolitan
Transmetropolitan is a cyberpunk comic book series written by Warren Ellis with art by Darick Robertson and published by DC Comics. The series was originally part of the short-lived DC Comics imprint Helix, but upon the end of the book's first year the series was moved to the Vertigo imprint as DC...

is based in a megacity simply referred to as The City
The City (Transmetropolitan)
The City is a fictional megacity which forms the main setting for the Vertigo comic Transmetropolitan by Warren Ellis. Located somewhere in the United States, the City is the largest metropolitan area in the futuristic world of the series , and the center of political and social culture. The City...

which seems to be an amalgamation of many cities along the East coast of America.
The Fifth Element
The Fifth Element
The Fifth Element is a 1997 French science fiction film directed, co-written, and based on a story by Luc Besson, starring Bruce Willis, Gary Oldman, and Milla Jovovich...

features a parody of New York City set in 2263. Buildings are so high that people use flying cars to get around and the ground level of the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

is obscured by pollution.
The 1973 film Soylent Green
Soylent Green
Soylent Green is a 1973 American science fiction film directed by Richard Fleischer. Starring Charlton Heston, the film overlays the police procedural and science fiction genres as it depicts the investigation into the murder of a wealthy businessman in a dystopian future suffering from pollution,...

, based on Harry Harrison's novel Make Room, Make Room
Make Room! Make Room!
Make Room! Make Room! is a 1966 science fiction novel written by Harry Harrison exploring the consequences of unchecked population growth on society. The novel was the basis of the 1973 science fiction movie Soylent Green, although the movie changed much of the plot and theme, and introduced...

, depicted New York City in 2022 with a population of 40 million. It is not said how large the city is, but the main character does make the comment that a wanted criminal is "over the city line in Philadelphia" implying that it has sprawled that far.
The sprawling metropolis featured in The Matrix
The Matrix
The Matrix is a 1999 science fiction-action film written and directed by Larry and Andy Wachowski, starring Keanu Reeves, Laurence Fishburne, Carrie-Anne Moss, Joe Pantoliano, and Hugo Weaving...

series of films can be considered a megacity. It is based on Sydney, Chicago
Chicago
Chicago is the largest city in the US state of Illinois. With nearly 2.7 million residents, it is the most populous city in the Midwestern United States and the third most populous in the US, after New York City and Los Angeles...

and Oakland, California
Oakland, California
Oakland is a major West Coast port city on San Francisco Bay in the U.S. state of California. It is the eighth-largest city in the state with a 2010 population of 390,724...

. While the city is never referenced by name in the films, in the MMORPG The Matrix Online
The Matrix Online
The Matrix Online was a massively multiplayer online game developed by Monolith Productions created by Richard Carroll. It was the official continuation of the storyline of the Matrix series of films. The game began closed beta-testing in June 2004 which was then opened for people who pre-ordered...

, the city itself is called the Mega City
Mega City (The Matrix)
Mega City is an enormous virtual megacity in which the inhabitants of the Matrix live their lives in the Matrix series. The City is a conglomeration of many cities, fused into one large city with a gigantic downtown and an impressive skyline....

.

External links

United Nations Department of Economic and Social Affairs, Population Division
e-Geopolis project Research Group, University Paris-Diderot
Lagos la Vida Loca by Mariana van Zeller
Mariana van Zeller
Mariana van Zeller is a Portuguese journalist and former correspondent for the Vanguard documentary series on Current TV.-Biography:Van Zeller studied International Relations at the Universidade Lusíada de Lisboa...

on Current TV
Current TV
Current TV, or Current, is a media company led by former U.S. Vice President Al Gore and businessman Joel Hyatt. Comcast owns a ten percent stake of Current's parent company, Current Media LLC....

Nov. 2007
Megacities Task Force
Maps of US Megacities from radicalcartography.net
IEEE Spectrum report on "Engineering the Megacity"
URBAN PLANET: Collective Identities, Governance and Empowerment in Megacities

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