I dont mean just to point you out, but this is not trure. Locations are NOT very open. Very few areas in the game even allow to veer off the main path more than a few feet.
I suppose I did not mean to say "very", but it is open enough that you can usually go anywhere you have been, and by the end of the game you can go almost anywhere plus a few extra areas. It is somewhat similar to FFVII and FFVIII, while they both have big worlds there is hardly any reason to veer off the main path.