GPS signals don't penetrate solid objects well. So other methods can be employed to add to it, such as Wifi and Mobile tower. Even if the GPS could be accurate, it does not support height. So different elevations are just going to produce an incorrect result.
Apps for malls and airports tend to use more precise wifi based locations and methods such as beacons. Many of the advertising boards have cameras (you can see them, if you look closely). These follow you around.
GPS signals are carried through waves at a frequency that does not move easily through solid objects. A GPS device relies on a series of satellites in order to determine where it is physically located. The signals sent from these satellites do not penetrate all kinds of barriers with ease. When you use a GPS inside a building, a wide variety of physical barriers and potential interference sources make it difficult for the device to pinpoint your location accurately.
From Why Doesn't GPS Work Inside a Building?
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