We've seen a lot of fan-made maps that try to capture the geography of George R. R. Martin's A Song of Ice and Fire series, but none have been quite so detailed as this monstrous map by one serMountainGoat — a map so thorough, it's impressed Martin himself.
This fan scoured the pages of Martin's books and looked at both canon and non-canon maps to try to create as accurate a picture of Westeros and beyond as he could. Since a few regions haven't been quite laid out in the books, he took some educated guesses, but the result is this gorgeous speculative map. You can see the entire — enormous — map at his site, as well natural and canon-only maps.
Even Martin was impressed with serMountainGoat's work, even if the map isn't quite accurate:
This is a very handsome map. And based on the information you have, it's quite good.
But of course there's lots of information you don't have, so it's not accurate. There are certain things — the geography and location of the Summer Islands, the placement of Qarth and the Jade Gates, everything east of Slaver's Bay and the Dothraki Sea... that you would have no way of knowing.
Martin actually has plans to release a full set of map posters in a boxed set titled Lands of Ice and Fire this coming October. But for now, this map will make more than an adequate substitute for the official thing.