IP geolocation

Databases combine registry records, network measurements and other sources. Country is usually reliable, region less so, and city is an approximation that can be off by a long way, especially on mobile networks.

VPNs and proxies break it entirely because the address reflects the server and not the person. Use it for broad decisions such as language or tax region, not to locate an individual.

Accuracy depends on the network. Fixed broadband in a city is often placed within a few miles, while a mobile address may map to a carrier hub far from the handset. Databases are rebuilt on a schedule and usually require credit to their source, so show the data date next to a result when a decision depends on it.