The Science of GPS

PrefaceThere was once a perfectly respectable way to become lost. You bought a paper map approximately the size of a dining-room table, unfolded it inside a moving automobile, covered the windshield with Ohio, accidentally tore Alabama away from Mississippi, argued with your spouse about whether Highway 98 was the blue line or the slightly darker blue line, and eventually stopped at a gas station where somebody named Earl gave you directions involving a water tower, an abandoned feed store, and a tree that had apparently been struck by lightning during the Eisenhower administration. Humanity survived this system for centuries. Then somebody decided that what we really needed was a constellation of atomic-clock-equipped spacecraft orbiting thousands of miles above Earth so a telephone could tell us to turn left at Walgreens.That is GPS.