Location: SF, CA don't call it frisco... Striker!!
Posts: 3,617
There are two books out that may help:
One is a recent release novel called "Wicked" about how the Wicked Witch of the West got that way.
Second is the book of Imaginary Places (by two Italian guys) that has a very extensive map of Oz, with some concise work-up on the entire Oz collection of novels (10 or 12.) It has recently been re-released by one of the big houses.