Intra-national trade

 The concept of gains from trade is of fundamental importance to economists. But don't be fooled into thinking that gains from trade are limited to international trade. The same theory that explains trade is just as relevant when talking about trade between individuals, cities and regions.

I was delighted to come across the table below in The Economist. The point it makes is simple, really. We often hear that the US depends less on international trade than many other countries: its imports and exports of goods add up to less than 25% of GDP (China’s are nearly 50%, Ireland’s, nearly 90%). But it's not that Americans are reluctant to trade; only that their domestic market is so big. The gigantic American economy would not be possible without massive amounts of trade - but those exchanges are perhaps better appreciated on a city- or regional scale:

America moved $20 trillion in merchandise in 2010, or more than 100% of GDP, if trade between cities is counted.