I haven't actually seen the map yet. I'm curious to see how it turns out. . . .
The person doing it is Isaac Stewart, a guy in one of my writing groups. He's a man of many talents, and works as an animator. He was very excited about Mistborn, and when I mentioned he could do the map, he was enthusiastic. I've heard a lot of what he's talked about with the book–doing a map that is based on old Victorian-era maps of London and Paris. We'll see what he comes up with!
EDIT: Now I've seen the maps!
Wow, Isaac did a wonderful job with these. One of the things I asked for was a round world map, and he really stepped up. I love the embellishments around the border and the illuminated manuscript type feel for it.
The city map is probably more important to the story. Oddly, I didn't actually do one of these when I was writing the novel. In fact, I only had a very basic sketch for the world map. That meant, of course, that when I sat down with one of the later drafts, some things were inconsistent. It also meant that a lot of things on the map weren't named, such as the gates.
I owe a lot to Isaac on this one. His intricate map is very detailed–each of those slums was hand-drawn with the insane twisting of all the little streets. He was the one who named the gates, building eight of them and naming them after the basic Allomantic metals. All and all, he did a fantastic job.