The Ars Arcanum is written in-cosmere by Khriss, who is from Taldain (White Sand). She and her associates can be seen in other books as well…if you know what to look for.
Khriss employs Nazh to go out and obtain artifacts, maps and stuff. You can see his notations on some of the ephemera that’s in the book. He gets the worst end of the deal.