What if Europe were the United States? is a question we've played with often on this page, at a safe distance from the crisis across the ocean. Far from a frivolous query, it helps us unpack the difference between a monetary experiment (their euro zone) and a true monetary and fiscal union (our "dollar zone"). The United States has plenty of intractable problems. Deciding whether to keep paying Medicaid for Mississippians after the state has a particularly disappointing year, or century, isn't one of them. Where we have laws and permanent transfer programs, Europe has debates over backstopping bonds and trading month-to-month bailouts for promises of fiscally ruinous austerity.

In short: If you want to understand why Europe looks like Europe, it can help to look at the United States.

This analysis from the Wall Street Journal brings color to the comparison by matching the size of U.S. metro economies to the size of European countries. I did not realize until today that the greater New York City economy was essentially the size of Spain; nor that Los Angeles was bigger than Switzerland; nor that Boston-Cambridge was larger than Greece.

The euro zone as a whole is about $17 trillion, according to the IMF, which makes it about 13 percent larger than the U.S. That means that Spain's share of the euro zone's economy (8.2%) is almost precisely equivalent to New York's share of the U.S. economy, when you include NYC's periphery in Northern New Jersey, Long Island, and parts of Pennsylvania. A useful analog when you hear stories about Spain's impending doom.