One of the first studies on a methodology to define and quantify the
metropolitan areas in Mexico was published by
El Colegio de México in 1978. In Luis Unikel's book "Urban Development in Mexico: Diagnosis and Future Implications", a metropolitan area was designated as "the territorial area that includes the political and administrative units from a central city, and any contiguous, urban political and administrative units with a direct socioeconomic interrelation with the central city, and viceversa". 12 metropolitan areas were identified, containing 25.6 percent of the national population. A 1993 study published by Mexico's National Institute of Public Administration (INAP), "Metropolitan and Regional Government and Management", defined a metropolitan area as "the physical or functional union of two or more
municipalities that contain a central city and its contiguous locations, or a central city and surrounding locations under its socio-economic influence", and increased the number of metropolitan areas to 37. • a group of two or more municipalities in which a city with a population of at least 50,000 is located in an urban area that extends over the limit of the municipality that originally contained the core city incorporating, physically or under its area of direct influence other adjacent predominantly urban municipalities, all of which either have a high degree of social and economic integration or are relevant for urban politics and administration • a single municipality in which a city of a population of at least one thousand is located and fully contained (that is, it does not transcend the limits of a single municipality) • a city with a population of at least 250,000 that forms a conurbation with other cities in the United States. The number of metropolitan areas increased to 55 under these criteria. CONAPO last reviewed the criteria in 2018, and from that date, a metropolitan area in Mexico is defined as: • a set of two or more municipalities where a city with a population of at least 100,000 is located, and whose urban area, functions and activities exceed the limits of the municipality, incorporating within its area of direct influence the predominantly urban neighboring municipalities, maintaining a high degree of socioeconomic integration. Also included are those municipalities that, due to their particular characteristics, are relevant to urban planning and policy for each metropolitan area. • municipalities with a city of more than 500,000 inhabitants. • municipalities with a city of more than 200,000 inhabitants located in the northern and southern border areas and in the coastal zone. • municipalities where state capitals are located, if they are not already included in a metropolitan area. These new criteria also introduced two groups of municipalities within a metropolitan area:
core, the location of the core city or cities in the area; and
peripheral, surrounding, urban areas with high degree of integration with the core. As per this last definition, there are currently 74 metropolitan areas in Mexico. 75.1 million people, 62.8 percent of the country population, live within a metropolitan area. ==Metropolitan areas beyond municipal borders==