I don't mind what you want to map but it should keep with what already has been mapped or detailed in any text so far. You can put the boundary through the death chaser swamp if you like. The roads and town names should exist tho as there has been text written about them.

The most northerly area which I have mapped a bit is in that region under this thread.
http://www.cartographersguild.com/showthread.php?t=2437

if you want to expand on then then go ahead.

Death chaser fen is a dangerous lizard man infested swampy area where the water is rising ever so slowly and the old road through the old Mere fort is now impassable so a new Mere fort has been established with a road to Mullion.

So as long as that is in place and the area does not become peaceful sylvan elf lands then you can annex that area.

Nobody has done much on the other side near to Roebuck Castle either. There were some plans to detail some ideas about an underground river connection which passed underneath Roeborder ridge and allowed the water to escape to the sea. We had some interesting ideas about a cave system down there with adventuring possibilities of protecting boats as they pass through the caves and lock system there.