Megacity, megapolis, or megalopolis is a general term for cities together with their suburbs or recognized metropolitan areas usually with a total population in excess of 10 million people. Whereas the term city may denote importance, population size or legal status of a place, the term megacity concentrates on size only.
In 1950 New York was the only such area. There are nineteen as of 2004; an increase from only nine in 1985. This has happened as the world's population moves towards the high (75-85%) urbanization levels of North America and Western Europe. It is not clear that any city exclusive of its suburbs exceeds 10 million.
United Nations projections indicate a slowing-down of the emergence of new megacities after 2005. However the expansion of the kind of highly-urbanised zones may remain an important trend, as seen in Boston-Washington (BosWash), Tokyo-Osaka, Johannesburg-Pretoria or Rio de Janeiro-São Paulo.
Many megacities have such a high population density that the cost of living is too high for those of average means to have a decent living space. Also, in such areas people are potentially more vulnerable to natural disasters and terrorism. Some consider this to be a problem of overpopulation, others merely as one of overconcentration.
In Canada, megacity refers informally to the results of having merged multiple cities that have grown together or the suburbs of an urban region into one large municipality. Cities so merged include Winnipeg (this merger antedates the term, and was called "Unicity" at the time), Halifax, Toronto, Ottawa, Hamilton, Sudbury, Montreal, Gatineau, Longueuil, Quebec, Saguenay, and Lévis. A Canadian "megacity", however, is not necessarily an entirely urban area, as many cities so named have both rural and urban portions, and do not necessarily constitute a large metropolis. Their definition is thus close to the metropolitan area concept.
Megacities in fiction
Fictional megacities feature in much dystopian science fiction, with cities such as the Sprawl and Mega-City One. The Sprawl is featured in William Gibson's Neuromancer, while Mega-City One is a megalopolis of 800 million people across the east coast of the United States, featured in the comic 2000 AD. The Matrix movies take place in a megacity, which is referred to merely as "the city" and is a virtual amalgamation of the generic features of contemporary cities. Planet-wide megacities have been depicted, including Trantor in Isaac Asimov's Foundation series of books and Coruscant in the Star Wars storyline.
Naming scheme for megalopolises
A number of megalopolises use portmanteau words as their names (e.g. ChiPitts).