The city is officially divided into 16 delegaciones (boroughs) which are in turn subdivided into colonias (neighborhoods), of which there are around 250; however, it is better to think of the city in terms of districts to facilitate the visitor getting around. Many older towns like Coyoacán, San Angel and Tlalpan got merged into the urban sprawl, and each of these still manages to preserve some of its original, unique character. The greater Mexico City metropolitan area is one of the world's largest and most populated, with an estimate of about 20 million people living in the region. It is shaped roughly like an oval of about 60 by 40 kilometers, 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 Ixtlacihuatl. Mexico City proper (with an estimated population of between 8 to 9 million) is located 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, and that is where most tourists will spend the majority of their time when visiting or staying in 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 (however, beware 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 2200 meters above the sea level. Some people not used to high places have experienced difficulty when breathing, however these symptoms fade a few minutes after arrival. Mexico City's night life is like all other aspects of the city; it's 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 decades-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. Also, when going out, check the date, since this is an important indicator of how full places will generally be, and how long you might have to wait to get in. Salaries are usually paid twice per month, the 30th/31st-1st, and the 14th-15th. On or right after these dates is when most Mexicans will go out, especially if pay day coincides with a weekend. In the more expensive places, people might leave for Acapulco or vacations farther afield during the summer and long weekends. Mexican weekends, in the sense of when it's common to go out drinking, are Thursday night to Sunday morning, and sometimes throughout Sunday. Mexico City weather is divided in two seasons, the dry, from November to April, and the rainy from May to October. Spring months are warm, while the summer months can vary from light to heavy rains especially in the late afternoon. Fall and winter dawns get really cold but with an amazingly clear sky. Temperatures range from 0°C in late October, November, December and January mornings, to 32°C in March, April and May during mid-day highs. http://wikitravel.org/en/Mexico_City