For urban centres outside metropolitan areas, that generate a similar attraction at smaller scale for their region, the concept of the regiopolis and respectively regiopolitan area or regio was introduced by German professors in 2006. In the United States, the term micropolitan statistical area is used.
A metropolitan area combines an urban agglomeration (the contiguous, built-up area) with zones not necessarily urban in character, but closely bound to the center by employment or other commerce. These outlying zones are sometimes known as a commuter belt, and may extend well beyond the urban zone, to other political entities. For example, Islip, New York on Long Island is considered part of the New York metropolitan area.
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 a single urban settlement; comparative statistics for metropolitan area should take this into account. Population figures given for one metro area can vary by millions.
There has been no significant change in the basic concept of metropolitan areas since its adoption in 1950, although significant changes in geographic distributions have occurred since then, and more are expected. Because of the fluidity of the term "metropolitan statistical area," the term used colloquially is more often "metro service area," "metro area," or "MSA" taken to include not only a city, but also surrounding suburban, exurban and sometimes rural areas, all which it is presumed to influence. A polycentric metropolitan area contains multiple urban agglomerations not connected by continuous development. In defining a metropolitan area, it is sufficient that a city or cities form a nucleus with which other areas have a high degree of integration.
See also the many lists of metropolitan areas itemized at § Lists of metropolitan areas.
The Australian Bureau of Statistics defines Greater Capital City Statistical Areas (GCCSAs) as the areas of functional extent of the seven state capitals and the Australian Capital Territory. GCCSAs replaced "Statistical Divisions" used until 2011.
In Brazil, metropolitan areas are called 'metropolitan regions'. Each State defines its own legislation for the creation, definition and organization of a metropolitan region. The creation of a metropolitan region is not intended for any statistical purpose, although the Brazilian Institute of Geography and Statistics uses them in its reports. Their main purpose is to allow for a better management of public policies of common interest to all cities involved. They don't have political, electoral or jurisdictional power whatsoever, so citizens living in a metropolitan region do not elect representatives for them.