At one point, Nick asks Gatsby which part of "the Middle West" he comes from, to which Gatsby replies "San Francisco". "I see," replies Nick, though in what tone of voice I can't say.
According to the note in one edition this reply shows Gatsby up as a liar, because of course San Francisco isn't in the "Middle West". But, given that neither Gatsby nor Nick is Mr Dumb from Dumbland, this doesn't seem very satisfactory. After all, they are in fact both Mid-Westerners, so why would Gatsby make such a stupid and obvious mistake? It would be a bit like someone from Winchester asking which part of Hampshire I came from, and my replying "Edinburgh".
So then we wondered whether "Middle West" had a wider geographical application in 1924 - one that stretched as far as the West Coast. Alternatively, maybe Gatsby was trying to make a mistake, for complex psychological reasons of his own - but even then it seems too obvious. That the mid-Western Fitzgerald thought San Francisco was in the mid-West seems still less likely; that he goofed in giving Gatsby such a stupid line, unthinkable! The only other possibility we came up with was that there's another San Francisco, possibly in Minnesota.
Which is it, Pumpkin Eaters?