The cartographers : a novel

This is a great book if you love mystery, murder, a bit of fantasy and of course, libraries! There is a murder in the cartography department of the New York Public Library. What's discovered is a priceless gas station map. What is so special about this map that people would kill for it? How does the map fit in with our main character's personal tragedy? Only by digging deep into the past will the mystery and murder be solved.