I've been looking at a couple of games and noticed that the transitions between tiles are handled somewhat different. I was wondering which methods are to be used in different situations and why. I'm currently using internal edges in a top-down game, and it's working out so far. But I don't want to run into problems later on, and have to redo the whole tileset. I noticed that platforming games mostly use the internal edges, and top-down games mostly use external and hybrid transitions. I can see how these tiles are used to create "depth" in top-down games, where the player apears to be standing in front of a wall for example. But it seems unlikely that such a small feature decides the entire method for tile transitions. You could always alter the bounding box to create the same effect.