Mexico City is the Federal District, capital of Mexico and seat of the federal powers of Mexico. It is a federal entity within Mexico which is not part of any one of the 31 Mexican states but belongs to the federation as a whole. Mexico City is the country's largest city as well as its most important political, cultural, educational and financial center.As an "alpha" global city Mexico City is one of the most important financial centers in North America. It is 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 was around 8.84 million people, with a land area of 1,485 square kilometres. According to the most recent definition agreed upon by the federal and state governments, the Greater Mexico City population is 21.2 million people, making it the largest metropolitan area in the western hemisphere, the third largest agglomeration, and the largest Spanish-speaking city in the world.The Greater Mexico City has a gross domestic product of US$411 billion in 2011, making Mexico City urban agglomeration one of the richest metropolitan areas in the world. The city was responsible for generating 21% of Mexico's Gross Domestic Product and the metropolitan area accounted for 34% of total national GDP. As a stand-alone country, in 2013, Mexico City would be the fifth-largest economy in Latin America—five times as large as Costa Rica's and about the same size as Peru's.The city was originally built on an island of Lake Texcoco by the Aztecs in 1325 as Tenochtitlan, which was almost completely destroyed in the 1521 siege of Tenochtitlan, and subsequently redesigned and rebuilt in accordance with the Spanish urban standards. In 1524, the municipality of Mexico City was established, known as México Tenochtitlán, and as of 1585 it was officially known as Ciudad de México. Mexico City served as the political, administrative and financial center 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 policies, such as abortion on request, a limited form of euthanasia, no-fault divorce and same-sex marriage.