GPS work 24/7 and in all weather conditions, although the actual low power 1625.55 Mhz radio signals travel line of sight. So that means it will not through the solid building, but it will be through the clouds and glass.
GPS is actually very accurate, even in densely populated cities, although it doesn't work indoors, the first is one of the world, like iBeacons technique is trying to correct. Outdoors, standard GPS receivers, for example, accurate to within 20 meters.
In addition to making use of GLONASS satellites and use higher precision parallel receiver, wearable devices and watches can also use WAAS (wide area augmentation system), it can keep your position to within 3 meters or DGPS differential GPS, GPS signal correction to a range of 3-5 m using a series of beacon.
It is worth noting that the GPS in the world there are four control and monitoring station.
Transmission of actual information including satellite ID code, the current date and time from the satellite atomic clocks, satellite state and track information, they show the satellite () and the rest of the satellite position at any given time.
Because you may be aware that once you have an accurate GPS signal, it can be used to track the speed accurately, to the destination, the distance of the sunrise and sunset.
So why don't always work perfect?
We are all in the beginning of the running, waiting for the GPS lock, looking for a satellite. Or realize no dot on Google maps in the right place.
GPS may not be accurate or slow because there are a lot of. There are several options: signal through atmospheric delay; Tall buildings or rock reflection and obstacles; The receiver clock inaccurate time; Building or natural way and close grouping of satellite.