... we declare all values in hash ...
Declare them as what? As Anonymous Monk pointed out above, the data you show is not a hash, it’s a list (of strings). Since you said this data is in a hash, I made a guess as to how the hash was contstructed. A hash is a collection of key/value pairs. Every key must have a value (and every value must belong to a key). I assumed that the data was stored as hash keys, so I supplied an undef value for each — but that could have been any value, as it isn’t used.
If your hash is really key/value pairs of the form: Chicago => 'USA' (another guess), adapting the answer I gave above should be quite straightforward.
Hope that helps,