Urban areas are created and further developed by the process of urbanization. Urban areas are measured for various purposes, including analyzing population density and urban sprawl.
Unlike an urban area, a metropolitan area includes not only the urban area, but also satellite cities plus intervening rural land that is socio-economically connected to the urban core city, typically by employment ties through commuting, with the urban core city being the primary labor market.
The concept of an "urban area" as used in economic statistics should not be confused with the concept of the "urban area" used in road safety statistics. The last concept is also known as "built-up area in road safety". According to the definition by the Office for National Statistics, "Built-up areas are defined as land which is 'irreversibly urban in character', meaning that they are characteristic of a town or city. They include areas of built-up land with a minimum of 20 hectares (200,000 m2; 49 acres). Any areas [separated by] less than 200 metres [of non-urban space] are linked to become a single built-up area.[7]