If the lady's put the wrong map in, it won't help (6)

I believe the answer is:

hamper

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But I can't explain it at all! Could you help me understand?

(Other definitions for hamper that I've seen before include "Obstruct with picnic basket" , "Kind of food basket, maybe for picnic" , "Food box; impede" , "Slow up - basket" , "Prevent free movement" .)

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