The definition of urban areas varies from one country to another. Some of the common bases of classification are the size of the population, occupational structure and administrative setup.
- Population Size: The lower limit of the population size for a settlement to be designated as urban is 1,500 in Colombia, 2,000 in Argentina and Portugal, 2,500 in U.S.A. and Thailand, 5,000 in India and 30,000 in Japan. Besides the size of the population, the density of 400 persons per sq km and the share of non-agricultural workers are taken into consideration in India.
- Occupational Structure: In some countries, such as India, the major economic activities in addition to the size of the population in designating a settlement as urban are also taken as a criterion
- Administration: The administrative setup is a criterion for classifying a settlement as urban in some countries. For example, in India, a settlement of any size is classified as urban, if it has a municipality, Cantonment Board or Notified Area Council.