In Rhumb Lines and Map Wars, Mark Monmonier offers an illustrated account of the controversies surrounding Flemish cartographer Gerard Mercator's legacy. He takes us back to 1569, when Mercator announced a clever method of portraying the earth on a flat surface, creating the first projection to take into account the earth's roundness. As Monmonier shows, mariners benefited most from Mercator's projection, which allowed for easy navigation of the high seas with rhumb lines - clear-cut routes with a constant compass bearing - for true direction. But the projection's popularity among nineteenth-century sailors led to its overuse - often in inappropriate, non-navigational ways - for wall maps, world atlases, and geopolitical propaganda.