Big cities pack a punch equal to some national economies. The GDP of Tokyo or New York, for example, is broadly similar to that of Canada, a G7 country. The two cities followed by Los Angeles will hold their position at the top of the table in 2020, according to forecasts from PricewaterhouseCoopers, an accountancy firm. However, London will pass Paris and Chicago to take fourth place thanks to buoyant expansion in business and financial services. At present, the top 15 city economies are dominated by those in the developed world. But by 2020, São Paulo will have elbowed its way into the premier league as part of a trend for those in emerging economies to move up the rankings.