Well, New York does have a big zoo...
Also!: I just thought of this. Umm, not sure if it's been said, but if it has I'll say it better. [/JK] So, I now think Isshu is New York again based on shape. But the thing is, the peninsulas are the right shape... but squished. EXACTLY! GF has been known to alter the location, like shift Johto so it lines with Kanto, rotate Hoenn, add part of Russia to Hokkaido to make Sinnoh, etc. So, taking New York and giving the peninsulas a little space wouldn't be that bad! So I think it's New York again, with the ferris wheel thing probably being based off the town near shanghai. But yeah... look at new york. Spread the peninsulas out a bit, straighten it a tad, and BAM! Isshu in a box!... Or on a screen. Whichever floats your boat. But the main other clues to NY are probably Hiun's art being the same as a pic of NY Harbor and the entire Victini deal.