A central business district (CBD) is the commercial and business center of a city. In larger cities, it is often synonymous with the city's "financial district". Geographically, it often coincides with the "city centre" or "downtown", but the two concepts are separate: many cities have a central business district located away from its commercial or cultural city centre or downtown, or even several CBDs at once. In London, for example, the "city centre" is usually regarded as encompassing the historic City of London and the mediaeval City of Westminster, whereas the City of London and the transformed Docklands area are regarded as its two CBDs. In New York City, Midtown Manhattan is the largest central business district in the city and in the world; yet Lower Manhattan, commonly called Downtown Manhattan, represents the second largest, and second, distinct CBD in New York City and is geographically situated south of Midtown. In Chicago, the Chicago Loop is the second largest central business district in the United States and is also referred to as the core of the city's downtown. Mexico City also has a historic city centre, the colonial-era Centro Histórico, along with two CBDs: the mid-late 20th century Paseo de la Reforma – Polanco, and the new Santa Fe.