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~ The geography of Hogwarts changed. Hagrid's hut is on the other side and all the way down a cliff. The whomping willow is also over a cliff. There were a lot of bridges and other things that just popped up. But who knows? Maybe they renovated Hogwarts over the summer.
This is actually what Hogwarts is meant to be like. Hogwarts is huge and Columbus didnt exand it in the first two movies. Alfonso got the scenery right. So this isnt really a mistake