Suburb

In some countries, including India, China, New Zealand, Canada, the United Kingdom, and parts of the United States, new suburbs are routinely annexed by adjacent cities due to urban sprawl. In others, such as Morocco, France, and much of the United States, many suburbs remain separate municipalities or are governed locally as part of a larger metropolitan area such as a county, district or borough. In the United States, regions beyond the suburbs are known as "exurban areas" or exurbs; exurbs have less population density than suburbs, but still more than rural areas. Suburbs and exurbs are sometimes linked to the nearby city economically, particularly by commuters.
Suburbs first emerged on a large scale in the 19th and 20th centuries, as a result of improved rail and road transport, which led to an increase in commuting. In general, they are less densely populated than inner city neighborhoods within the same metropolitan area, and most residents routinely commute to city centers or business districts via private vehicles or public transit; however, there are many exceptions, including industrial suburbs, planned communities, and satellite cities. Suburbs tend to proliferate around cities that have an abundance of adjacent flat land.