What's the map itself carved from? That must've taken ages to get the coastline accurate!
The map is 10mm blue foam used for underfloor insulation, just carved with a scalpel.
I freehanded the coastline on a big piece of paper, laid it over the top of the foam and just cut through the paper....took 15 mins or so.
There is a certain degree of interpretation with the islands...the shapes vary from the maps in the books, to the World of Fire & Ice etc. Not every little speck has made it onto the map yet, and I can always add a bit more texture to the coastline in the next stage.
Mountains will be carved from blue foam, and be impassable other than via a road. The limited number of roads in Westeros makes for an interesting campaign - the importance of river crossings such as the Twins is obviously clear, and of choke points such as Moat Cailin - and clearly having a fleet gives a real mobility advantage.