By Chris Woolston

T he next time your car directs you to the nearest taco stand, thank Bradford Parkinson, a pioneer of the Global Positioning System. The retired Stanford University professor envisioned GPS in the 1960s and, with air force colleagues, made it a reality by the mid-1970s. From the start, he insisted that the satellite-guided system should serve the public as well as the military. He discussed his creation in San Luis Obispo, Calif. (35°16'58" N, 120°39'45" W).

Q Did you foresee GPS's everyday uses?
A In 1978, I made sketches of a GPS display in a car. I imagined a screen with an arrow telling you to turn right in 100 feet. It took 17 years for that to actually happen.

Q What does the device do best?
A I'm really interested in robotic tractors. Guided by GPS, they can spread fertilizer to the nearest inch. There are also hundreds of units monitoring movement of faults in the West, accurate to a tenth of an inch. In the future, cars could use GPS to run on autopilot. It would really cut down on rear-end collisions.

Q Is there a dark side to GPS?
A Some stalkers use it to track their victims—anything like this can be abused. But there's another downside. I recently used GPS while driving in Europe. You lose all the learning that goes along with using maps or visual cues to navigate.

Q Will GPS units become throwaway gadgets like pocket calculators?
A They already are. The chips cost $15. Cell phones with GPS go for about $45.

Q So have you thrown out your maps?
A I use a handheld when I go hiking, but I still need a map to consider other routes and to get a sense of my surroundings.

Q How many GPS units do you own?
A Ten, at least.