The minimum population required to constitute a city differs between countries. In the United States, an urban area is defined as a settlement where 2,500 or more people reside.
In some countries, a city is classified as having a population of 20,000 or more. In others, this threshold may be far lower. Simply counting the number of people is not the only way to define a city. Urban areas can be distinguished by population, population density, the distribution of public utilities or the percentage of the population not dependent on agriculture for income. The notion of a metropolitan area commonly includes an urban center and surrounding areas that are economically integrated with the city.