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Demographia defines an urban area (urbanized area agglomeration or urban centre) as a continuously built up land mass of urban development that is within a labor market (i.e. metropolitan area or metropolitan region), without regard for administrative boundaries (i.e. municipality, city or commune). Except in Australia, the authorities use a minimum urban density definition of 400 persons per square kilometer (or the nearly identical 1,000 per square mile in the United States). Demographia uses maps, satellite photographs to estimate continuous urbanization. Demographia also uses small area population data, where available, to match population estimates to urban land area. National census authority data are presented in Australia, Canada, France, Norway, Sweden, the United Kingdom and the United States. Census of India urban agglomerations are not used in some cases because the geographical size of constituent units (municipalities) often includes large rural (non-urban) areas. [1]
Sources for population estimates and land area definitions are coded by letter in the cited report, respectively.
- A: National census authority data agglomeration data (land area or population).
- B: Demographia land area estimate based upon map or satellite photograph analysis.
- C: Demographia population estimate from lower order jurisdictions, including reduction for rural areas.
- D: Population estimate based upon the United Nations agglomeration estimate.
- E: Demographia population estimate from national census authority data.
- F: Other Demographia population estimate, such as from unofficial local reports.
- L: Demographia population estimate from local authority data.
- N: Combined urban area using national census authority data.
- W: Population estimate based upon the World Bank Urban Area 2015 estimate.
The projected year (2017) population estimate is further calculated from the base year population estimate using population growth rate based upon the United Nations population growth rate with some exceptions.
The estimates are quite different from the list of World's largest urban agglomerations produced by the United Nations that reports inconsistently on urban geographic, despite its reference to agglomerations. This is evident, for example, in Manila, Kuala Lumpur, Jakarta, Seoul and Moscow, where the UN data are for political jurisdictions, rather than urban areas. In other cases, the UN data is for metropolitan area, which are larger than urban areas (such as in Brazil). Finally, the United Nations data is incomplete, excluding some significant urban areas (such as Essen–Düsseldorf in Germany).[ citation needed ]
Urban areas are confined to a single nation, unless there is freedom of movement (including labor) between the adjacent nations. Currently, this condition is met only between some continental nations of the European Union and Switzerland (e.g. Lille–Kortrijk in both France and Belgium, Aachen–Vaals in both Germany and Netherlands, Saarbrücken–Forbach in both Germany and France, Geneva–Annemasse in both Switzerland and France, and Basel–Lörrach–Saint-Louis in Switzerland, Germany and France). Thus, Detroit–Windsor in both the United States and Canada, and San Diego–Tijuana in both the United States and Mexico are not treated as single urban areas. Moreover, Shenzhen–Hong Kong is treated as separate urban areas, principally because labor movement between the two is limited, with the former within China and the latter a special administrative region of China. [ citation needed ]
According to the report, there are 1,040 identified urban areas in the world with 500,000 or more population as of 2017. Demographia released along with the report include a disclaimer that this list of data is compiled on best available information, the vary nature of which is changing rapidly and quality is improving as it becomes available, yet still remains highly variable between nations. Appropriate caution is therefore advised.
