In recent years it has reduced its relative importance in domestic manufacturing, but has kept its dominant role in the country's economy thanks to an expansion of its tertiary activities.

[4] As of 2020[update], 21,804,515 people lived in Greater Mexico City,[5] making it the largest metropolitan area in North America.

During conquest of the Aztec Empire the dikes that protected the city from recurrent floods were destroyed and colonial authorities preferred to drain the water of the lake, which was, for the most part, shallow.

The valley of Mexico is surrounded by mountains on all four sides creating a basin with only one small opening at the north, trapping all exhaust emissions of the city.

If the IMECA values reach a critical level, an environmental contingency is declared whereby Hoy No Circula is extended to two days per week, industrial activities are reduced, certain gas power plants shut down, and elementary school entry hours are changed.

(trillion MXN)[1] (billion USD) From 1940 and until 1980, Greater Mexico City experienced an intense rate of demographic growth concurrent with the economic policy of import substitution.

Greater Mexico City's main industries are now related to trade, financial services, insurance companies, telecommunications, informatics and transportation.

Mexico City proper alone produces $170 billion or 17% of the nation's Gross Domestic Product, larger than any of the states.

[5] Approximately 72% (12.2 million) of the State of México's population live in municipalities that are part of Greater Mexico City's conurbation.

Since then, and through a policy of decentralization in order to reduce the environmental pollutants of the growing conurbation, the annual rate of growth of the agglomeration has decreased, and it is among the lowest of all metropolitan areas in Mexico.

Even though some of these municipalities have some of the wealthiest neighborhoods of the metropolitan area, there is a huge contrast with peripheric low-income suburbs known as "marginal zones" or "lost cities".

Some examples are the wealthy suburb of Tecamachalco next to El Molinito shanty town, both in Naucalpan, or Chamapa next to Bosque Real Country Club in Huixquilucan.

Municipalities to the east of Mexico City, such as Nezahualcóyotl, Ecatepec, Valle de Chalco or Chimalhuacán have lower indexes than those located to the west, but also present high HDI values.