I am doing something wrong in my tessellation.
I have a material that is essentially a bunch of tessellated tiles. As Shown Below :
However, if I just move the camera over to show you another angle, where that edge connects with another edge (which has a different texture) - You can see that a very noticable gap appears here :
These to polygons are from the same mesh by the way - that ledge is not a separate mesh that has been brought in separately or anything.