Drawn half a millennium ago and then swiftly forgotten, one map made us see the world as we know it today... and helped name America. But, as Toby Lester has discovered, the most powerful nation on earth also owes its name to a pun. Almost exactly 500 years ago, in 1507, Martin Waldseemuller and Matthias Ringmann, two obscure Germanic scholars based in the mountains of eastern France, made one of the boldest leaps in the history of geographical thought - and indeed in the larger history of ideas. Near the end of an otherwise plodding treatise titled Introduction to Cosmography,...