It's just a function of how the game loads in world chunks. It seems to work like minecraft where chunks of the world are not generated until you get within a certain distance, at which time they are generated, and that's when you get those long-ish pauses. You'll see them all the time when you're exploring into the "fog of war" because it's always generating those new chunks. You should also notice that running around in explored areas have no such stutter.