Metaphorically, if you lay out a conventional Eurocentric map with the Atlantic Ocean in one piece and the Pacific Ocean split into two pieces at opposite ends, and you take the low-income and middle-income nations that lie wholly or partly inside the tropics, you get a big sweep of countries from China in the upper right through Southeast Asia and the ASEAN Archipelago through India and Southwest Asia and Africa and South America and the Caribbean and parts of North America and if you step back and squint, and especially if at its tallest stretch as it passes through Africa you kind of focus on Central Africa, its kinda like an arc. I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.
