Overview

Locations on Earth are determined by a gridwork of lines, one set marking distance north or south of the equator and the other marking distance east and west of the Prime Meridian, running through Greenwich, England. For centuries, determining one's longitude, that is, one's position east or west of Greenwich, was nearly impossible, leading to the loss of life, ships, and property. This problem was finally solved by John Harrison (1693-1776), an Englishman, with his development of a highly precise clock called a chronometer. This invention revolutionized travel by sea, with repercussions that lasted until the 1990s.

Background

Today, for a few hundred dollars, virtually anyone can purchase a hand-held unit that, by detecting signals from an artificial constellation of satellites, will obligingly display one's latitude, longitude, and altitude with a precision of a few meters or less. The...