Those of you who played Tales of the Abyss probably remember that towns and dungeons were formed from a number of separate blocks connected together. (For example, the city of Baticul was divided into five blocks.)
In Vesperia, Bandai-Namco is taking advantage of the Xbox 360's power to make the map blocks many times larger than those in Abyss. You could call it a "semi-seamless" design.
Vesperia's map setup is basically the same block-based one as Abyss -just now each one of them is significantly larger. You'll see just how large when you explore the towns and cities of Terca Lumireis.