What you've found is likely a break between the slices of the map that make up the world, sometimes they relate to zone phasing. Otherwise I think they're also there to help off load people to another instance of the zone. There are similar ones throughout the game. A friend of mine and I came across one near a lamp post in Auridon where if we passed it at a certain angle people would disappear from the screen. Given the proximity to the lamp post we since came to calling these areas pocket Narnias. You can walk back across the division to the other instance of the zone. Unfortunately things and creatures in the other slice will disappear since they won't exist in the other instance.