I downloaded the map for Google Earth and I was pleasantly surprised to notice that you named that one island Lincoln Island. Jules Verne fan? Or simply chose the name because of Abe?
About maps. I created some compasses (north symbols) for maps. You can check them here right: http://brtkr.extra.hu/downloads.php?cat_id=14 SVG and PNG. You can use them on your work because they're free.
I'd suggest you check out www.cartographersguild.com for a group of fantasy/alternate earth/other mapping enthusiasts. There are a few users there who use inkscape, and having more (or even some tutorials or tips) would be nice.