Depending on how "approximate" is acceptable, I've found that using timezone names can be a good proxy for location. As most users have their timezones set correctly it's more consistent and private than IP or GPS.

I've made a library for my own use cases that does this (https://github.com/mcteamster/virgo), but it's also pretty straightforward to parse the city/state name out of the timezone and look it up somewhere.