Metro-Matrix Theory » External Relevant References » 05 PriceWaterHouseCoopers

PriceWaterHouseCoopers: The largest city economies in the world
  PriceWaterHouseCoopers UK Economic Outlook July 2009
  Rankings of global cities by population are common, but while population statistics are important, they are only part of the story: leading cities such as London, New York, Paris and Tokyo are major economies in their own right, of
a size greater than medium-sized national economies such as Sweden and Switzerland.

Cities are also centres of innovation, creativity and culture, as well as focal points for government, finance, business services and corporate headquarters in their respective countries (and sometimes also their regions in the case of financial centres like London in Europe, or political centres like Brussels in the EU).

However, data are much less readily available on the overall size of city economies in terms of their total output, particularly outside the OECD countries2.