For a really great discussion on "uncharted territory" in life and in fiction, check out Michael's post of yesterday. He did such a super job that he's freed me up to go four-wheelin' on the subject.
Like Michael, I love maps, but for me, I go for the "oldies but goodies," that is, the ones that are set in the time and location that I write about. Since my Silver Rush series is set in real 19th century towns and cities, maps are near and dear to my heart and help me get oriented in yesterday's worlds.
One wall in my home office has two super-sized bird's eye maps of Leadville, Colorado: one from 1878, the other from 1882. You can click on the dates and see them in the Library of Congress and zoom around for the details. One thing you'll no doubt notice right away is how the city grew by leaps and bounds in those three years.
I also have cemetery maps, Sanford Fire Insurance maps, and a few more virtual and paper reproductions tucked in folders here and there. In my opinion, there's no such thing as "too many" maps!
Now, I'm moving out of the familiar realm of 1880 Leadville into... you guessed it... uncharted territory, that is, San Francisco, California, 1881(ish).