Mexico City is the current capital and largest city in the country of Mexico. It is the current seat of the Powers of the Union but the Mexican federal Congress, which is controlled by the 31 free and sovereign Mexican States, can change the location of such seat if it desires to do so. Mexico City is also known as the Federal District , a federal entity within Mexico which is not part of any one of the 31 Mexican states in particular, as it belongs to the federation. It is the most important political, economic and cultural center in the country. It is also considered one of the two most important financial centers in Latin America, (the other being São Paulo, Brazil). It is also considered a global city. Located in the Valley of Mexico, a large valley in the high plateaus at the center of Mexico, at an altitude of 2,240 metres , the city consists of sixteen boroughs.
The 2009 estimated population for the city proper exceeds 8.84 million people, and with a land area of 1,485 square kilometres , Mexico City is the most densely populated city in the world. According to the most recent definition agreed upon by the federal and state governments, the Mexico City metropolitan area population is 21.2 million people, making it the largest metropolitan area in the Americas and the third largest agglomeration in the world. The city had a Gross Domestic Product of $390 billion USD in 2005, making Mexico City the 25th largest economy in the world, richer than industrialized countries such as Taiwan and developing countries like Iran. It is also ranked as the eighth richest city in the world. According estimates, as of 2008, the city proper, as opposed to the metropolitan area, had a nominal income per capita of $25,258 USD, above the national average, and on par with the GDP per capita of Portugal, which has a comparable population, and significantly above nations such as South Korea, and Czech Republic.
The city was originally built as Tenochtitlan by the Aztecs in 1325 on an island of Lake Texcoco, which was almost completely destroyed in the siege of 1521, and subsequently redesigned and rebuilt in accordance with the Spanish urban standards. In 1524, the municipality of Mexico City was established, known as México Tenustitlán, and as of 1585 it was officially known as Mexico City. Mexico City served as the political, administrative and financial centre of a major part of the Spanish colonial empire. After independence from Spain was achieved, the Federal District was created in 1824.
After years of demanding greater political autonomy, residents were given the right to directly elect the Head of Government and the representatives of the unicameral Legislative Assembly by popular vote in 1997. Ever since, the left-wing Party of the Democratic Revolution has controlled both of them. In recent years, the local government has passed a wave of liberal reforms such as abortion on request to any woman up to 12 weeks into a pregnancy, a limited form of euthanasia, and LGBT rights. Mexico City was the first city in Latin America to legalize same-sex marriage.
Urbanization has had a serious negative effect on the city's environment. Pollution, dwindling water supply and poor air quality have been some of the city's largest problems improved in recent years by regulating the circulation and renovating the vehicle park. Many factors such as industrial growth and a demographic boom (from 3 million in 1950 to some 20 million in the metropolitan area today) have contributed to this situation. More than 3.5 million vehicles are now in the city streets. Although crime rates are still an issue of concern, by 2006 they had been reduced by almost 40% from 1994's historic highs.