The global positioning system, invented a couple of decades ago, works
by having a bunch of satellites circling the earth broadcasting the
time. Just the time. Because radio signals travel at the speed of light,
which is not infinite, your GPS receiver can tell from how late the
signals are how far away the satellites are. If it has at least 3
signals, it can figure out exactly where you are in space. If it has a
data connection, it can then query a map database to find out where you
are on the Earth. If it doesn't have a data connection but it does have
map data, either because it is cached or because you deliberately
uploaded it to your phone, it can still figure out where you are.
The system can break down in 2 basic ways:
1. No signal from GPS satellites. GPS signals are available all over the
globe. Most of the satellites are in geosyncronous orbit around the
equator but enough of them are not so you can still get a GPS signal at
the poles. However, the radio signals from the satellites is very weak
and you might not even be able to pick it up in a mobile home. In a
parking garage, probably not
2. No map data. If your location is not in a mpa database, if you don't
have access to a map database, or if the map data is wrong, your phone
won't know where you are. It should still be able to give you GPS
coordinates but that won't help most people most of the time.
Note: I have talked only about GPS systems. Your phone can also
triangulate it's position from cell phone towers and even wifi signals.
Google has made a map of as many of the wifi signals it can in the
world. So if you called the wifi in your house "blindGuysAreSexy", it
might be able to tell someone where they are based on that alone.
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