The first major theme of the book is the outlined biography of William Smith, particularly how his experiences growing up in England shaped his obsession with mapping the natural world. The first part of the book provides vignettes of Smith's life and independent studies.

The second major theme of the book is cartography. Winchester details the history of mapmaking, beginning with ancient times and moving to the exploration era initiated by Spain, Portugal, and the British Empire. Winchester provides various perspectives on how cartography evolved and why maps prior to Smith's time contained minimal information or geological elements. The maps created before Smith's time that did contain geological information were done so mostly to support imperialist ambitions to exploit minerals and natural resources in other countries. Therefore, geological maps and topography were rooted in capitalist ventures rather than a serious, thorough study of the earth's geology.

Another prominent theme in the book is William Smith's groundbreaking work in geology. In fact, Smith is considered the "father of geology." In Winchester's book, readers are presented with examples of how cartography and geology are inextricably linked. There was a growing need for topography- and geology-focused study in cartography during Smith's time, and he addressed these needs while also positing that geological study was important as a stand-alone field.

Another theme in the book is Smith's dogmatic nature when pursuing his work, and how his obsession with cartography and setting the foundation for the field of geology led to financial ruin. In this light, Smith is seen as a prophet or genius who sacrificed his personal life in order to birth a new field of science.