The method that Google uses on a landline to determine location is based on where it thinks the IP address of the user is based. As IP addresses are dynamically allocated, these can change and the latest records in the system may not match the true physical location (never has).
The only true way to determine someone's location on a landline based service is if they have a GPS hooked up to their computer.
Never be afraid to back yourself when trying new things, just always make sure you have 3 escape routes if things go wrong.
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