Does anyone consider a royalty fee as well? Or is that where the rights come in? For example do you charge a certain fee for a particular initial print run and then if it goes to another run is it renegotiable? If a book series went Da Vinci (wherever you are in the world you're never more than a metre away from a copy of The Da Vinci Code) I'd imagine anyone who sold artwork for a few hundred quid would be a bit sick, especially if it made it onto the big screen.

On the other hand unless something is self published I understand that a lot of publishers use their own artists to produce artwork, including maps. An author having a map commissioned may cause potential conflicts in the future (e.g. if a publisher's artist produced something similar to the author's artist) which may or may not jeopardise the chances of being accepted for publication.

None of this really matters to me as I don't ever envisage myself being a professional cartographer. Unless someone wants to use my fish blueprint, complete with puns, for a multi-billion dollar film franchise of course