Well, Skyblade, it appears that I have solved the map problem.
The answer is very simple, actually.
FFTA Ivalice does not have to cover the whole territory of the former Ivalice (FF XII and FFT)
The FF XII map I used is not in-game, but still, if you look at the peninsula in the frame, you'll notice the similarities between it and the FFTA Ivalice.
As for the FFT map, the peninsula seems to be in a different location, but that can be explained by the fact that science has been thrown centuries back from the before-catastrophe time, Geography included.
Another proof to the connection between all the Ivalices (them all being one world) are the writings on the FFT map (if they aren't just Japanese names of the locations and countries, of course, but I doubt it). They look very similiar to the writings we've seen in Mewt's Grimoire next to the drawings of the races, which was created in the before-catastrophe times. So if those writings are really of the same language, they serve as a proof to the connection of the worlds.
The fact that none of the four could read the writings in the Grimoire is explained by the fact that this language/writing style was discarded with the invention of Latin letters (remember, Ritz thought that 'Alta Oron Sondus Kameela' was Latin or something).
This gave me another interesting thought about the Grimoire, by the way. What if the 'later additions' ('in Latin or something') were made in Latin letters so that nobody could read it and unseal the magic before it's time? If the Grimoire was made in times when Latin letters were just invented and only few could read them, then it's no wonder that the sealing spell was written in them.
I have to work some more on this thought, though.
Thank you for your comments, people.
Selena