A metropolitan area is a region consisting of a populous urban core with a high density of employment plus surrounding territory that is socio-economically linked to the urban core by commuting. A metropolitan area is also sometimes known as a commuter belt or a labor market area.
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' metro area. While it is not the same city, its socioeconomic identity is intimately tied to that of Los Angeles.
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".
There has been no significant change in the basic metropolitan area "concept" since its adoption in 1950, though significant changes in geographic distributions have occurred since, and is expected to further evolve through time. Because of the fluidity and evolution of the "term" metropolitan statistical areas, the colloquial reference by the general population and media to define an MSA is with a more familiar reference to "metro service area, metro area, metro, or MSA" and widely intimated to mean the total geographic area inclusive of not only a well known city population, but also its inner city, suburban, exurban and sometimes rural surrounding populations, all which are influenced by employment, transportation, and commerce of the more largely well known urban city.
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.
"Statistical Divisions" are defined by the Australian Bureau of Statistics as areas under the unifying influence of one or more major towns or a major city. Each State's capital city and the Federal capital of Canberra forms its own Statistical Division, and the population of the Statistical Division is the figure most often quoted for that city's population.
Statistical Districts are defined as non-capital but predominantly urban areas. By far the most important of these is the city of Newcastle, New South Wales, and others can be found in the Gold Coast, Queensland, and in Cairns, Queensland.
The statistical divisions that encompass the seven capital cities are commonly, though unofficially, called "metropolitan areas", borrowing the common term that is used in the United States and in Canada.
The European Union's statistical agency, Eurostat, has created a concept named Larger Urban Zone (LUZ). The LUZ represents an attempt at a harmonised definition of the metropolitan area, and the goal was to have an area from a significant share of the resident commute into the city, a concept known as the “functional urban region”.
In India, the Census Commission defines a metropolitan city one having a population of over 4 million. Mumbai, Delhi, Chennai, Kolkata, Bengaluru, Hyderabad, Ahmedabad, Pune, Nashik, Surat are the ten cities that qualify. Residents of these cities are also entitled to a higher House rent allowance. The figure only applies to the city region and not the conurbation.
In Japan a metropolitan area would be toshiken (都市圏, lit. bloc of cities).
The Office of Management and Budget defines "Core Based Statistical Areas" used for statistics purposes among federal agencies. Each CBSA is based on a core urban area and is composed of 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.
This concept of a "megalopolis" was first proposed by the French geographer Jean Gottmann in his book Megalopolis, a study of the northeastern United States. One prominent example of a megalopolis is the Northeast megalopolis consisting of Boston, Hartford, Greater New York City, Philadelphia, Wilmington, Delaware, Baltimore, Washington, D.C., and their vicinities. Two other prominent megalopolises in North America are as follows:
1. In California and Mexico, Ventura County, Los Angeles County, Orange County, San Diego County, part of Riverside County, part of San Bernardino County, and the northwestern part of the State of Baja California del Norte. There are hundreds of cities and towns in this megalopolis, with the largest ones being Los Angeles, Long Beach, Irvine, Anaheim, San Diego, and Tijuana.
2. In Ontario, Canada, its largest city, Toronto, is a component of Ontario's Golden Horseshoe, which includes other major cities in Southern Ontario such as Hamilton, Brantford, and Niagara Falls. The Golden Horseshoe has about eight million people, which is about one-fifth of the entire population of Canada. Also, adjoining the Golden Horseshoe is the metropolis of Buffalo in the State of New York.
The world's largest megalopolis is probably is the Taiheiyō Belt (the Pacific megalopolis) of Japan on southeastern Honshu that consists of the metropolis of Tokyo, Shizuoka, Yokohama, Nagoya, Osaka, Kobe, Okayama, Yokosuka, Hiroshima, Fukuoka, Kure, and their surrounding cities and towns. Major means of ground transportation in Japan such as its railroad network (for both passengers and freight), many expressways, and the "Shinkansen" bullet train are concentrated in this region, which also includes the northern shore of the Inland Sea of Japan. This is a highly-industrialized part of Japan, and it is also the location of its most important seaports in Japan - such as at Yokohama, Osake, Kobe, Hiroshima, and Kure - and its most important international airports - such as at Tokyo and Osaka. The population of this megalopolis can be considered to be as high as 83 million people, depending on where one draws its boundaries.
Guangdong Province's Pearl River Delta is a 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.
The megalopolises in Europe are the Rhine-Ruhr metropolitan region (pop. 11.5 million) in Germany, the Milan metropolitan area (pop. 7.4 million) in Italy, the Randstad in the Netherlands (pop. 7.4 million), the Flemish Diamond in Belgium (pop. 5.5 million), Ile de France in France and the metropolitan area of London and Moscow, as well as several 'smaller' agglomerations, such as the Meuse-Rhine Euregion, the Ems-Dollart Region, 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.
Africa's first megalopolis is situated in the urban portion of Gauteng Province in South Africa, comprising the conurbation of Johannesburg, and the metropolitan areas of Pretoria and the Vaal Triangle, otherwise known as the PWV.
It has been suggested that most of southeastern England, the Midlands, and parts of northern England will someday evolve into a megalopolis dominated by London. Clearly when usage is stretched this far, it is remote from the traditional conception of a city.
Megacity is a general term for metropolitan areas which usually have a total population in excess of ten million people. In Canada, "megacity" can also refer informally to the results of merging a central city with its suburbs to form one large municipality. A Canadian "megacity", however, is not necessarily an entirely urbanized area, since many of its named "cities" have both rural and urban portions. Also, 10 million inhabitants is an unreasonbly-high number for Canada. Moreover, Canadian "megacities" do not constitute large metropolitan areas in a global sense. For example, Toronto has a metropolitan population of about five million people, but is part of a much larger metropolitan region called the Golden Horseshoe, which has about eight million people.
The census population of a metro area is not the city population. However, it better demonstrates the population of the city. Los Angeles may only have a city population of near four million, but depending on the definition, it has a metropolitan area population of either 13 million, or 18 million people in its combined statistical area. A major question is whether or not to include San Diego and Tijuana.