America's cities are economic powerhouses.
Reddit user atrubetskoy created a map showing just how important cities 
are to the American economy. atrubetskoy took gross metropolitan product data —
the total of economic
activity in a metropolitan area, and the equivalent of gross domestic product for cities
— and noted that the top 23 cities have GMPs that add up to about to half of overall
United States GDP.
The orange regions fall in those top 23 metro areas, and the blue region falls outside
them, accounting for the other half of GDP:
Here are the top 23 cities, and their 2012 gross metropolitan products, from the Bureau of Economic Analysis: