thumb|Àrea metropolitana de TòquioEl concepte d''''àrea metropolitana''' o '''zona metropolitana''', també anomenada '''àrea urbana''' o '''aglomeració urbana''', es refereix a la regió urbana que envolta una ciutat principal i diverses ciutats satèl·lits. Una ''megalòpoli'' és l'àrea metropolitana formada per dues o més ciutats principals i diverses ciutats satèl·lits i també pot rebre el nom de ''conurbació''. El concepte va ser utilitzat per primera vegada pel geògraf francès Jean Gottman, dins el seu llibre ''Mégalopole''.

==Les àrees metropolitanes més grans==
Aquest és una llista de les àrees metropolitanes més grans del món amb estimacions per al 2005. Aquest és un tema controvertible difícil de quantificar, ja que, a diferència d'altres subdivisions nacionals, no hi ha fronteres definides per a les àrees metropolitanes. Les dades d'aquesta llista provenen del Report d'Urbanització Mundial de les Nacions Unides [http://www.un.org/esa/population/publications/wup2003/2003WUPHighlights.pdf] (2003). Les àrees metropolitanes inclouen les àrees suburbunes que envolten a les ciutats principals, així com altres ciutats importants properes que en conjunció funcionen com una sola conurbació. 
thumb|Mumbai
thumb|Ciutat de Mèxic
thumb|Rio de Janeiro
# Tòquio, Japó, 35,2 milions
# Ciutat de Mèxic, Mèxic, 19,0 milions
# Nova York, Estats Units, 18,4 milions
# São Paulo, Brasil, 18,3 milions
# Mumbai, Índia, 18,3 milions
# Delhi, Índia, 15,3 milions
# Calcuta, Índia, 14,3 milions
# Buenos Aires, Argentina, 13,3 milions
# Jakarta, Indonèsia, 13,2 milions
# Xina 12,6 milions
# Dhaka, Bangladesh, 12,6 milions
# Los Angeles, Estats Units, 12,1 milions
# Karachi, Pakistan, 11,8 milions
# Rio de Janeiro, Brasil, 11,5 milions
# Osaka, Japó, 11,3 milions
# El Caire, Egipte, 11,2 milions
# Lagos, Nigèria, 10,9 milions
# Beijing, República Popular de Xina, 10,8 milions
# Manila, Filipines, 10,7 milions
# Moscou, Rússia, 10,7
# París, França, 9,8 milions
# Istanbul, Turquia, 9,6 milions
# Seül, Corea del Sud, 9,5 milions
# Xina, 8,7 milions
# Chicago, Estats Units, 8,7 milions
# Lima, Perú, 8,2 milions
# Londres, Regne Unit, 7,6 milions
# Bogotà, Colòmbia, 7,6 milions
# Teheran, Iran, 7,4 milions
# Xina, 7,2 milions

==Les àrees metropolitanes en relació amb la demografia mundial==
===Percentatges===
D'acord a l'estudi realitzat per les Nacions Unides, la proporció de persones que viuen a àrees metropolitanes amb una població superior als 10 milions d'habitants, és petita en comparació amb la població mundial: el 2003 era al voltant del 3%. Però, aquesta xifra augmetarà els pròxims anys, i s'espera que el 2015 arribi al 4%. El percentatge de població mundial que vivia el 2003 en ciutats amb menys de 500,000 habitants és del 25%. És a dir, un gran percentatge de la població mundial és urbana. 

===Nombre d'àrees urbanes===
El 2005 el nombre d'àrees urbanes amb més de 5 milions d'habitants era 46. El 2015 en seran 61. El nombre d'àrees urbanes amb més de 10 milions d'habitants era 20 el 2003, el 2015 en seran 22.

thumb|Metropolitan area in Western [[Tokyo as seen from Tokyo Tower]]
thumb|right|A 3D rendered image of the [[San Diego-Tijuana metropolitan area, a bi-national urban agglomeration.]]
A '''metropolitan area''' is a large population center consisting of a large cities and their zone of influence.  One or more large cities may serve as its hub or hubs, and the metropolitan area is normally named after either the largest or most important central city within it.

==General definition==
A metropolitan area usually combines an agglomeration (the contiguous built-up area) with peripheral zones not themselves necessarily urban in character, but closely bound to the center by employment or commerce; these zones are also sometimes known as a '''commuter belt''', and may extend well beyond the urban periphery depending on the definition used. It is mainly the area that is not part of the city but is connected to the city. For example, Pasadena, California would be added to Los Angeles, California's metro area. While it isn't the same city, it is connected.

The core cities in a polycentric metropolitan area need not be physically connected by continuous built-up development, distinguishing the concept from conurbation, which requires urban contiguity. In a metropolitan area, it is sufficient that central cities together constitute a large population nucleus with which other constituent parts have a high degree of integration. 

In practice the parameters of metropolitan areas, in both official and unofficial usage, are not consistent. Sometimes they are little different from an urban area, and in other cases they cover broad regions that have little relation to the traditional concept of a city as a single urban settlement. Thus all metropolitan area figures should be treated as interpretations rather than as hard facts. Metro area population figures given by different sources for the same place can vary by millions, and there is a tendency for people to promote the highest figure available for their own "city". However the most ambitious metropolitan area population figures are often better seen as the population of a "metropolitan region" than of a "city".  
===Differences in terminology by country ===
The term metropolitan area is sometimes abbreviated to 'metro', for example in metro rail system of the city. Although it can be compared in composition to many of the world's metropolitan areas, in France the term for the region around an urban core linked by commuting ties is an ''aire urbaine'' (officially translated as "urban area"). In Japan that would be .

===Country official unique definitions===
==== Australia ====
thumb|right|[[Perth, Western Australia|Perth is arguably the most isolated metropolitan area in the world.]]
In Australia, Statistical Divisions (SDs) are defined by the Australian Bureau of Statistics as areas under the unifying influence of one or more major towns or cities. Each capital city forms its own Statistical Division, and the population of the SD is the most-often quoted figure for that city's population. Statistical Districts are defined as non-capital but predominantly urban areas. The statistical divisions that encompass the capital cities are commonly though unofficially called 'metropolitan areas'.<ref>''[http://www.abs.gov.au/Ausstats/abs@.nsf/7d12b0f6763c78caca257061001cc588/32eb1b908521ad75ca2571220079feee!OpenDocument#M 1217.0.55.001 - Glossary of Statistical Geography Terminology, 2003]'', Australian Bureau of Statistics, 2003</ref>

==== United States ====
The counties which comprise that core as well as any surrounding counties that are tightly socially or economically integrated with it.  These areas are designated as either metropolitan or micropolitan statistical areas, based on population size; a "metro" area has an urban core of at least 50,000 residents, while a "micro" area has less than 50,000 but at least 10,000.<ref>[http://www.census.gov/population/www/estimates/metroarea.html Metropolitan and Micropolitan Statistical Areas],yeah boii thats one hell of a fact ay ;) U.S. Census Bureau</ref>

==Additional terms==
At the turn of the 19th century only 3 percent of the world was urbanized. During the 20th and into the 21st century the presence of humans in urban areas has increased dramatically. Within the first quarter of the 21st century it is expected that more than half of the world's population will live in urban areas, if this is not already the case.<ref>[http://www.economist.com/surveys/displaystory.cfm?story_id=9070726 The world goes to town]</ref> 

By 2025, according to the ''Far Eastern Economic Review'', Asia alone will have at least 10 hypercities, those with 20 million or more, including Delhi (~20 million), Jakarta (24.9 million people), Dhaka (25 million), Karachi (26.5 million), Shanghai (27 million) and Mumbai (33 million).<ref>[http://www.atimes.com/atimes/Front_Page/HE20Aa01.html Planet of Slums by Mike Davis]</ref> Lagos has grown from 300,000 in 1950 to an estimated 15 million today, and the Nigerian government estimates that city will have expanded to 25 million residents by 2015.<ref>[http://www3.nationalgeographic.com/places/cities/city_lagos.html Lagos, Nigeria facts - National Geographic]</ref> 

If several metropolitan areas are located in succession, metropolitan areas are sometimes grouped together as a '''megalopolis''' (plural ''megalopoleis'', also ''megalopolises''). A megalopolis consists of several interconnected megalopolis is a metroplex (short for metropolitan complex) or conurbation.

This concept was first proposed by the French geographer BosWash megalopolis consisting of Boston, Providence, Hartford, Newark, Wilmington, Baltimore, Washington, and vicinity.

The biggest one is the Taiheiyō Belt (the Pacific Megalopolis) in Japan consisting of Tokyo MA, Shizuoka MA, Nagoya MA, Osaka MA, Okayama MA, Hiroshima MA, Fukuoka MA and vicinity. Guangdong Province's Pearl River Delta is a huge megalopolis with a population of 48 million that extends from Hong Kong and Shenzhen to Guangzhou. Some projections assume that by 2030 up to 1 billion people will live in China's urban areas. Even rather conservative projections predict an urban population of up to 800 million people. In its most recent assessment, the UN Population Division estimated an urban population of 1 billion in 2050.<ref>[http://english.people.com.cn/200409/16/eng20040916_157275.html China's urban population to reach 800 to 900 million by 2020: expert]</ref>

The megalopoleis in Europe are the Ruhr Area in Germany, the Randstad (Knooppunt Arnhem-Nijmegen and Brabantse Stedenrij are counted with the Randstad) in the Netherlands, the Flemish Diamond in Belgium, Ile de France in France and the metropolitan area of London, as well as several 'smaller' agglomerations, such as the Meuse-Rhine Euregion, the Ems-Dollart Euregion, the Lille-Kortrijk-Tournai Euregion and Metropoly of Upper Silesia in Poland (17 cities around Katowice with a total population of over 2 million). Together this megalopolis has an estimated population of around 50 million.