Vexillology

I love how many african nations share a distinctive style in their flags. You often see the flag of a country you're not familiar with and you can tell it's from Africa. I wonder why that is, on the one hand it's natural that nearby countries would share a lot of symbology, but this effect doesn't strike me as so pronounced in other regions of the world, except the nordics, and maybe parts of the caribbean. Probably my biases showing though.