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Some Google employees have mentioned that it's there to improve GPS times. The devices already have a latitude+longitude estimate from cell towers and WiFi, and the barometer adds an altitude estimate.

You would have thought that "ground level" (based on the latitude and longitude estimate) would be a pretty good starting estimate for altitude in most cases.


In a modern urban environment I think this is becoming less and less so.

Living in a metropolitan area for me at least mean I spend quite a lot of my time in an Nth floor apartment, Mth floor office, and commute by subterranean subways and elevated train tracks, walkways and highways.


The difference in altitude between the subway and the top floor of an apartment building isn't really very far though, when observed from a GPS satellite that's 20,000 km above you.


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