GPS is one of the most reliable systems there is. There are redundant constellations of satellites run by different companies in different countries.
1. GPS refers specifically to the system run by the united states government. The generic term is GNSS
2. Even though there are multiple GNSS systems out there, and modern phones support multiple, it's unknown whether the same applies to other systems. Supporting multiple systems costs more money, so I suspect hardware vendors might skimp on that, especially when the benefits are so marginal.
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1. GPS refers specifically to the system run by the united states government. The generic term is GNSS
2. Even though there are multiple GNSS systems out there, and modern phones support multiple, it's unknown whether the same applies to other systems. Supporting multiple systems costs more money, so I suspect hardware vendors might skimp on that, especially when the benefits are so marginal.