At last, the worlds of cartography, vexillology and population statistics meet! This map was inspired by earlier maps of the US, with its states renamed for countries with a similar GDP (see posts #131 and #135).
It shows each US state covered by the flag of a country with a population of comparable size. This map was made by James Richards, who also sent in a list of the pairs of US states and flags of corresponding countries. But I agree with him that “unlabeled, it’s a fun test of your knowledge of nations, can you guess them all?”
Update: the full list is posted as provided to me by Mr Richards in comment #36.