The phenomenon of the Edge City is one of most visible results of suburban migration. When a suburban settlement reaches a certain mass, services and institutions usually associated with the urban environment tend to appear: office buildings, sports arenas, and cultural institutions can now be found in suburban environments. Eventually, the former suburb becomes a self-contained pseudo-urban entity known as an Edge City.
Traditionally, suburban environments have been seen as refuges from the chaos of the metropolis. Suburbanites worked in the city, returning to the safety and tranquillity of the suburbs at night. With the formation of Edge Cities, however, the city's usual functions (employment, cultural events, and so on) have been taken over by the suburbs. One can live, work, and play in the Edge Cities, never needing to cross the border into the city proper. This creates a vicious cycle: as the city centre's utility decreases, the problems (poverty, crime, etc.) which caused the suburbanites to leave the city in the first place can only increase.
Although not exclusive to the United States, Edge Cities are most prominent in American urban environments. Two notable examples of metropolitan areas which contain highly developed edge cities are Baltimore and Los Angeles. Both cities, although vastly different in size, are made up of an impoverished, low-population-density urban centre surrounded by a ring of prosperous Edge Cities. In some urban environments, however, the process appears to be reversing: gentrification and urban renewal have helped to draw former Edge City-dwellers back to the city centre.