Glampkoo

Never mind, I got it. All I had to do, was select the "ocean" region, reverse the selection so it would select all the landmass, with AA disabled, delete it. Then globally fill any of the transparent or landmass region with any colour (I selected gray). The result is exactly what I wanted.

I'm creating a fictional map and I want the end goal to look like this. I already have the map completed and cleaned up, the problem is the size of the borders. They are too thick. I'm looking for a technique or filter that does something like this..