As the title indicates, this is a novel about cartographers, that is PhD geography scholars. One of the settings is the Map Division of NYPL. (Or "the NYPL" as it's referred to in the book, but I doubt that any NYPL employees employ the "the") The protagonist, Nell Young, is the product of a marriage between cartographers, or as we learn Cartographers. When we meet her, her mother is long dead, and her father recently so. She'd had a falling out with him over what's referred to as "The Junkbox Incident." The Incident caused Nell's father to turn on her, turning her out of her internship and likely scholarly career in the Map Division. To these nerds, all maps are special, but we learn that one workaday gas station map from the 1930s is very special. 

The mystery thriller with a handful of murders tells the story of the map and its mystical properties. Nell and her ex and her mentors are compelling. I love people with a niche interest being niche and interesting!