hmmm..... haven't done this as my current game is only in a "region" - so I don't have an actual world map for the Mountain Realms map - however if I had to have a world map AND full region maps of everything (which may seem a bit overkill - I'd probably just select some regions and map those) I think I'd make the world map first - rough sketch of everything. Then i'd divide it into manageable sizes and map those in high res, finally when all those where done I'd shrink them to make a new world map.
Another attack route could be to make the world outline in vector but I think the first idea would work best for me