See attached picture, if you zoom into the southeast corner of the grid up to about 3/4 zoom, a bunch of unrezzed grids appear. When standing on the edge of the main sim it looks like just the edge of the world, except for the land drops suddenly instead of just ends, you can fly out to the landmass too.
There's 12 water sims connecting 70 land sims to the main grid. I dunno, 4 sims wide wasn't what I envisioned as a 'land bridge.' Either way, there they are.

