Mexico City has been an iconic example of an extensive metropolitan area since the 14th century when it became the largest city in the American continent. Its continuous population growth and concentration of economic and political power boomed in the 1930s when the country's involvement with global markets benefited the national financial industry. Currently the fifth largest city in the world, with a population of 21 million inhabitants (17.47% of national population) living in 16 districts and 59 municipalities, the urban area continues to expand receiving 1,100 new residents daily. The division of the city is derived from a strong socially and economically segregated population connected by its interdependence, that manifests into spatial arrangements where luxury areas coexist alongside slums. Its development around a core called “El Zocalo” derives from the historic, cultural and political relevance of a central plaza, as well as its contemporary concentration of economic power, currently housing 80% of all national firms.