I love exploring the world of this novel through my sketchbook. A couple reasons why. For one, it's a great way to flesh out scenes, and specifically, details of the world that can zip through your head before you get to jot them down. Another benefit is getting to see things that will never make it into the book. Like this guy here.
Why would you create something that's not going in the book? Seems like a waste of time. Quite the opposite for me. Even if much of what I create doesn't make the cut, it helps give the world of the Conjurian an added sense of reality. It becomes a real living, breathing organic system. And that's key for a fantasy book. I certainly don't want the reader feeling as if the book is just a bunch of made up places and creatures strung together. Rather I want to give them the sensation that they have stepped through a window into a world that already was and continues to be. A rabbit's hole made from bound pieces of paper.
Creating such an experience is the joy and torment of writing.