How do you measure the wealth of nations? Two ways: compare national GDPs, or size up per-capita GDPs. Those two categories don't necessarily correspond: countries can be rich, but their citizens poor – or vice versa.

Check out this map of our Solar System to see the crucial difference between both.

The U.S. is the Sun, because it is both the world's biggest economy (national GDP over $18.5 trillion) and has the highest per-capita income of the world's largest economies (the average annual income in the U.S. is just over $57,000).

The nine planets in the Solar System (yes, Planet Nine... even if we don’t see you, we are looking at you) symbolize the nine next-biggest economies in the world. In two ways:

Firstly, their distance to the Sun expresses the difference in per-capita GDP. The UK, with the second-biggest per-capita GDP, is Mercury, the planet closest to the Sun. Following the planets in clockwise order, we end at Planet Nine/India: furthest from the Sun, smallest per-capita GDP.

Secondly, the size of the planets reflects the size of overall GDP. China is Uranus, 7th planet from the Sun, because it is 7 places behind the U.S. in per-capita GDP. But it is the second-biggest heavenly body on this map, because of the huge size of its total GDP. Third in size is Japan, last is Brazil: Uranus is closer than Planet Nine (because Brazil's per-capita income is higher), but also smaller (because India's total GDP is higher).

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