City At Night

In 2004, a joint effort between CONAPO (National Council of Population), INEGI and the Secretariat of Social Development (SEDESOL) agreed to define metropolitan areas as either:
- The group of two or more municipalities in which a city with a population of at least 50,000 is located whose urban area extends over the limit of the municipality that originally contained the core city incorporating either physically or under its area of direct influence other adjacent predominantly urban municipalities all of which 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 million is located and fully contained, (that is, it does not transcend the limits of a single municipality).