For of course everyone should trade more with Tim Worstall. But there is a specific point to be made here. Trade is, as we know, how we all get rich. And I am not suggesting that North Korea's lack of trade with one middle aged Englishman is what makes the poor benighted nation poor. I am though pointing out the fact that we can see that they are poor by how little they trade with this one specific middle aged Englishman.

  That's quite a famous photo of the Korean peninsula from space. As you can see, North Korea has almost no lighting that can be seen. South Korea quite massively more. And as I'm sure I've told you old hands around here before, in my day job I deal with one of the metals that is used in making those sorts of light bulbs that can be seen in these sorts of photos from space. I've even been told (but cannot confirm) that 50% of the light that you see in these pictures comes from bulbs using the material that I handle. No, I don't mean as in it's just the same metal that I handle, I mean as in the actual pieces of it that I have done.

No, this has not made me a fabulously wealthy man, do not worry, but it is still true. We can see, from the absence of light at night, where the poor places in the world are and this is a symptom of their not trading enough with Tim Worstall. For if they did they would have the bulbs to light up the night.

That the poor parts of the world don't trade enough with anyone is why they are poor. But I will admit to a certain egotistic frenzy about the way that we measure this poverty, the absence of light at night, which means that we measure such poverty by the absence of trade with, umm, me. No, really, we do!

GDP growth is often measured poorly for countries and rarely measured at all for cities or subnational regions. We propose a readily available proxy: satellite data on lights at night.