At the end of the show, C. J. emerges from the meeting with the stunned abstraction of one who has experienced a continental shift, so to speak, in her basic worldview. After the episode aired, sales of the world map based on the Peters projection reportedly skyrocketed overnight.

In Rhumb Lines and Map Wars: A Social History of the Mercator Projection, Mark Monmonier, a professor of geography at Syracuse University, offers an in-depth, balanced, and at times quite technical study of Mercator’s projection specifically, and the history and methods of map projection in general. The complexity of some portions of the book is hinted at in the title—a rhumb line is a nautical term, defined by the Oxford Universal Dictionary as “any one of the set of lines drawn through a point on a map or chart and indicating the course of an object moving always in the same direction.”

This little book exhibits a rare—indeed, almost mutually exclusive—combination of elements: scholarship, readability, and usefulness. Monmonier’s purpose is to address the Mercator map and its critics with what he calls “informed skepticism,” a goal he achieves by clearly representing all sides of the argument. Although not a textbook on map projection, the book is a handy introduction to the subject and contains as much information as the nonspecialist is likely to need.

As any cartographer will tell you, no flat map of the world can accurately represent all distances. Mercator’s projection was devised primarily for navigators, and we’re all familiar with his equatorial-projection maps that show Greenland bigger than China, India smaller than Scandinavia, and an amazingly massive Antarctica. Monmonier’s book is the story of how map projections devised for use during the age of sail were also used well into the twentieth century as land maps. Since the age of sail (1450–1850) ran parallel to the age of European conquest and hegemony, these projections came under fire during the culture wars of the last few decades.

The first chapter offers an overview of the mathematics of map projection and its history. Chapter two covers early sailing charts (the portolan tradition), and chapter three discusses Mercator’s life and works. Chapter four is useful to the scholar and the collector, as it details how Mercator’s maps were reproduced over time, what was lost or altered in those reproductions, and to what extent they are accessible or available today. The fifth chapter discusses how later discoveries and contributions by mathematicians such as Edward Wright (1561–1615), Henry Bond (ca. 1600–1678), Thomas Harriot (1560–1621), and Richard Norwood (1590– 1675) promoted a wider use of Mercator’s projection in navigation. Chapter six reveals, however, that because Mercator sailing requires reliable methods for taking bearings and determining position (including an accurate marine chronometer), it wasn’t until the eighteenth century that his projection became “the gold standard of marine cartography.” Chapter seven examines how military uses of maps influenced the development of map projections (initially used around the turn of the twentieth century to aim long-range, rapid-fire field guns), and chapter eight discusses similar developments in response to the beginning of long-distance flight.

The final three chapters focus on the social history part of the book’s subtitle. In the 1990s, according to Monmonier, the Peters map became the “emblem of diversity awareness, marketed as the cornerstone of a catholic cartography in which dissimilar images of the world promote cultural sensitivity.” It was hoisted as a standard by postcolonial deconstructionists “poised to slay dead dragons.” In the end, Monmonier convincingly concludes, “Peters’s proponents ignored decades of pointed criticism of the Mercator map by academic cartographers and its wholesale abandonment by map publishers in the 1940s. Their simplistic scenario linked the Mercator map to an unsympathetic cartographic establishment and aligned the Peters map with pro–Third World organizations…To help their readers understand the controversy, newspapers and magazines juxtaposed examples of the Mercator and Peters world maps—as if these were the only choices—and used visual propaganda to put professional cartographers on the defensive.”

Mercator-projection maps still decorate classroom walls, mostly because the supply catalogs upon which teachers rely still promote them. Like Monmonier, I am not convinced that the worldviews of thinking people are significantly influenced by a wall map, whatever its method of projection. After reading this book carefully, and weighing the arguments, the reader will realize that perhaps the best solution is simply to go out and buy a globe.