Would that be "book" as in player hand-out or "book" as in submitting to a publisher?

I'm going to assume you're asking about the first situation. In that instance, I'd probably supply a sub-regional map (one spanning the area commonly known to the characters), perhaps a few key area local maps (major towns and the like) and, of course, the background information as far as recent history, legends and myths, current events and the like. Basically all the stuff that the characters would have learned growing up in that particular area of the world.

GW