Megacity
Some sources identify the Greater Tokyo Area as the largest megacity in the world,[5][8] while some others give the title to the Pearl River Delta in China.
[22] In many poor countries, overcrowded slums exhibit high rates of disease due to unsanitary conditions, malnutrition, and lack of basic health care.
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.
[27][28] 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.
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.
[30] 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.
This increase has happened as the world's population moves towards the high (75–85%) urbanization levels of North America and Western Europe.
The majority of these are located in informal settlements which often lack sufficient quality housing, sanitation, drainage, water access, and officially recognized addresses.
[citation needed] People who live in slums or informal settlements often have minimal or no access to education, healthcare, or the urban economy.
[40][41] 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.
[43] In 2002, research showed that children and families were the largest growing segment of the homeless population in the United States,[44][45] and this has presented new challenges, especially in services, to agencies.
[49] 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.
Air pollution is the introduction into the atmosphere of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or damages the natural environment.
[54] Many urban areas have significant problems with smog, a type of air pollution derived from vehicle emissions from internal combustion engines 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.
Whether megacities can develop sustainably depends to a large extent on how they obtain, share, and manage their energy and material resources.
[55] Megacities are a common backdrop in dystopian science fiction, with examples such as the Sprawl in William Gibson's Neuromancer,[56] and Mega-City One, a megalopolis of between 50 and 800 million people (fluctuations due to war and disaster) across the east coast of the United States, in the Judge Dredd comic.
[58] Fictional planet-wide megacities (ecumenopoleis) include Trantor in Isaac Asimov's Foundation series of books and Coruscant (population two trillion) in the Star Wars universe.
