tl;dr: start from the beginning of this series for a wallop of a finish
I have found that even when a series of romance novels tends to be a collection of “standalones”, reading previous books is an asset to the enjoyment of all followups. The books build on each other, creating a universe of world-building in a small section of the world, introducing people, places, and a sensibility that carries through to the rest of the books.
So while The Cartographer is a fantastic book, with a solid arc for both characters, a rich world, and sexy smut, there’s something missing for someone that begins reading a series from the final book. However, this book is simply fantastic, and I will be going back to read the previous 5.