Why do you think District 4 is in Mexico? Does the first book say something about the waters rising and Panem coming out of what was left of the USA? I'm not against the idea but I always thought the Capital was as far west at the country went and the old southern states being as far south as it reached.
It says coming out of North America - people usually forget about Canada and Mexico, haha.
I like this map:
and the reasoning for it can be found here.








