Help with hash table

Hi, given the $variable  with 2 properties

Country   City

England   London

USA         Washington

FranceParis

When i query an AD  user and get 

$user.city= 'London'

How can i compare it against $variable.city so it equals the $variable.country as England in this case?

I think is with hash tables but i am not sure how to implement it.

Thanks