मैं अकेला ही चला था जानिब-ए-मंज़िल मगर लोग साथ आते गए और कारवाँ बनता गया - Purnesh Upadhyay

again not true
gps stands for global position satellite
its basically a satellite receving and sending datas to give us exact location
it will be more accurate at higher altitude rather than on ground bcoz on ground we have so many distrubances like wall,building,roof etc so it solves the purpose,but not very accurate on ground for speed measurements
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height of 10km{or 35000ft} there are no obstructions apart from aircraft shell itself,so its more accurate than on ground
i wont say my data was 100% accurate, but as announced in flight that we were flying at mach0.85 at 38000ft, so it was above 1000kmph for sure

On most commercial aircraft, you'll have a hard time.There's just not enough window space and the aluminum skin of the aircraft blocks the GPS signals. And if you follow the rules and turn off electronic devices, you'll lose the fix that you had when you had on the ground. This makes it even harder for the GPS to lock.
Most phones will have trouble getting GPS signals without a cell connection since they are designed to rely on the availability of data network assisted GPS most of the time.
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physical altitude limit may not apply on aircraft. However, I believe there's also, interestingly, an intentional technical limit on what most GPSs can do. The reason for this is that the US government doesn't want Iran and North Korea etc to be able to build missiles that use GPS for guidance, so they have mandated that GPS chips should not work at heights or speeds that are clearly in typical range of what aircraft can do.
Hope that's useful.....