The blank spots on a map and the legends that speak of terrae incognitae are among the most seductive sirens of the cartographic imagination. They hint at the existence of unknown lands, yet tell us nothing about what they are or what they might be like. Do such lands even exist? How many types of terrae incognitae are there? What does it mean, and what has it meant, to mark a land as unknown? Why do so many maps of the last five centuries insist on reserving a place for unknown geographies? This book navigates the cartographic unknown, exploring its contribution to the history of knowledge and geographical culture.