A city is a relatively large and permanent settlement. Although there is no agreement on how a city is distinguished from a town within general English language meanings, many cities have a particular administrative, legal, or historical status based on local law.
For example, in the American state of Massachusetts an article of incorporation approved by the local state legislature distinguishes a city government from a town. In the United Kingdom and parts of the Commonwealth of Nations, a city is usually a settlement with a royal charter. Historically, in Europe, a city was understood by some to mean an urban settlement with a cathedral. The belief in this distinction is also common in England, where the presence of a cathedral is thought by many to distinguish a 'city' (sometimes called a 'cathedral city') from a 'town' (which has a parish church); the belief is incorrect (Chelmsford, for example, became a city only in 2012, but had a cathedral for most of the 20 century).
Cities generally have complex systems for sanitation, utilities, land usage, housing, and transportation. The concentration of development greatly facilitates interaction between people and businesses, benefiting both parties in the process. A big city or metropolis usually has associated suburbs and exurbs. Such cities are usually associated with metropolitan areas and urban areas, creating numerous business commuters traveling to urban centers for employment. Once a city expands far enough to reach another city, this region can be deemed a conurbation or megalopolis.
There is insufficient evidence to assert what conditions gave rise to the first cities. Some theorists, however, have speculated on what they consider suitable pre-conditions, and basic mechanisms that might have been important driving forces.
The conventional view holds that cities first formed after the Neolithic revolution. The Neolithic revolution brought agriculture, which made denser human populations possible, thereby supporting city development. The advent of farming encouraged hunter-gatherers to abandon nomadic lifestyles and to settle near others who lived by agricultural production. The increased population-density encouraged by farming and the increased output of food per unit of land created conditions that seem more suitable for city-like activities. In his book, Cities and Economic Development, Paul Bairoch takes up this position in his argument that agricultural activity appears necessary before true cities can form.