Mapping Hacks

Chapter 5, Mapping with Gadgets

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along similar principles. Russia still maintains its own satellite-based GPS,

known as GLONASS. More recently, other nations, including the European

Union and China, are working together to field their own satellite-based glo-

bal positioning system, called Galileo, which they hope to have online by

2007.

One curious side note about satellite-based GPS stems from

a prediction of Einstein’s General Theory of Relativity that

time should travel more slowly as one gets closer to a large

gravitational source, such as a planet. In fact, the atomic

clocks in orbit on board GPS satellites actually do run faster

than their Earth-bound counterparts, to the tune of 12

microseconds a year. While you can blink and miss a dura-

tion that brief, it turns out that this discrepancy causes a

noticeable error in GPS triangulation, and the satellite clocks

must be corrected for the difference. This strange fact makes

for an interesting and oddly practical verification of Ein-

stein’s well-known theory!

Leave your own breadcrumbs: tracklogs and waypoints. Most handheld GPS

units provide an easy way to save a marker to your current position. These

are called waypoints, and they are great at allowing you to capture your own

experiences. If you press and hold the “mark” button, the GPS will display a

screen allowing you to name the waypoint. A tracklog is a series of position

points that ...