The Guild of Lines
The cartographers who decide what is real enough to be drawn.
In the Reach, a place is not legally a place until the Guild of Lines has drawn it. Property, borders, taxes, and inheritance all depend on Guild maps, which makes the Guild one of the most quietly powerful institutions on the continent.
Guild cartographers swear an oath to draw only what they have measured. Edda broke that oath once. That's why she was expelled, and it's why her master trusted her with the map that does not stop at the Wall.