Practicality.

The majority of European Americans in the eighteenth century lived within one hundred miles of the seacoast. Virtually everyone living there was linked inescapably to the great Atlantic commercial routes, from the urban merchants to the inland farmers, from governors to slaves. Manufactures of every sort-clothing, tools, pottery-came from Europe, paid for with American timber, tobacco, fish, and grain. And none of this extensive trade could take place without the ability to get a ship safely and efficiently across three thousand miles of trackless ocean. The science of navigation made American trade possible. It was an ancient art, but significant advances in astronomy and instrumentation in the eighteenth century transformed it into a science, one in which mathematics and the latest astronomical information were tools of the trade.

One's Place in the World.

For centuries seafarers had used maps that...