If men buys shoes at the Shoes Department, the nearest department would be Men's Inner were socks are, right? If ladies buy tops and blouses, adjacent to it would of course be jeans! An indirect suggestive selling! This very principle would answer why department stores have a general category per floor.
In most department stores this would be the set-up:
Ground Floor - Men's. Where you can find Men's Apparel, Men's Underwear, Men's Jeans, and Men's Accessories.Why at the ground? Studies show that men don't usually go up the floors to shop. Makes sense right?
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Second Floor - Ladies'. Unlike men, even if you put the Ladies' Floor at the 10th floor they would still go there and shop! Here you can find Ladies' Apparel, Jeans, Lingerie, Shoes, and Accessories.
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Supermarket - This is usually located in a separate building or on the lower floors. Effectively paired up with food stalls and bakeries that satisfies that churning after a long stroll for the groceries.
So as you can see, right categorizations is the right key for sales.