Mexico City (Spanish: México, Ciudad de México, or D.F.) is the capital city of Mexico, and the largest city in North America by population.
The greater Mexico City metropolitan area is one of the world's largest and the largest city by population in North America, with an estimated 26 million people living in the region. It is shaped roughly like an oval of about 60 by 40km, built on the dry bed of Lake Texcoco, and surrounded on three sides by tall mountains and volcanoes such as the Ajusco, the Popocatepetl and the Ixtaccihuatl. Mexico City proper (with a population of 8.8 million as of 2010) is in the Federal District (Spanish: Distrito Federal or D.F.), a federally-administered area (that is, not part of any Mexican state) which acts as the capital of Mexico. The rest of the metropolitan area extends beyond it into Mexico State, which surrounds D.F. on three sides. Legally and practically speaking, Mexico City is the same as the Federal District, much in the same way the city of Washington is the same as the District of Columbia in the United States' capital city. The Federal District is where most tourists will spend the majority of their time while visiting the city.
Mexico City is divided up into 16 delegaciones, similar to the boroughs of New York, which in turn are divided into "colonias" (neighborhoods), of which there are about 250. Knowing what colonia you're going to is essential to getting around, almost all locals will know where a given colonia is (but note that there are some colonias with duplicate or very similar names). As with many very large cities, the structure is relatively decentralized, with several parts of the city having their own miniature "downtown areas." However, the real downtown areas are Centro, the old city center, and Zona Rosa, the new business and entertainment district.
The city is located 2,200m above mean sea level. Some people may have breathing difficulties at high altitudes and experience difficulty when breathing. The altitude is equivalent to more than 7,200 ft. This is far higher than any metropolitan area in the United States. If you live closer to sea level, you may experience difficulty breathing due to altitude and pollution. Air quality has, however, been improved in the last few years.
Skyline of Reforma skyscrapers
Mexico City's night life is like all other aspects of the city; it is huge. There is an enormous selection of venues: clubs, bars, restaurants, cafes, and variations and combinations thereof to choose from. There is incredible variation, from ultramodern lounges in Santa Fe and Reforma, to centuries-old dance halls in Centro and Roma. There are also pubs in Tlalpan and Coyoacán and clubs of every stripe in Insurgentes, Polanco, Condesa and the Zona Rosa.
Images from Mexico City