How do geolocation services determine location based on IP address?

Geolocation services based on IP addresses operate using databases that match IP addresses to geographic regions. These databases are compiled from various sources: internet service provider data, public registries, IP distribution information, and user reports.

Working principle:

1. The obtained IP address is looked up in the database.
2. By matching the IP range, the country, region, city, and sometimes more precise coordinates are determined.
3. The result is returned to the client.

Accuracy depends on the relevance and completeness of the database. For example, an IP allocated to a mobile operator may indicate the region where the operator is registered, not the actual location of the user.

Example of usage in C# with the MaxMind GeoIP2 library:

using MaxMind.GeoIP2;

var reader = new DatabaseReader("GeoLite2-City.mmdb");
var city = reader.City("128.101.101.101");
Console.WriteLine(city.Country.Name); // for example, United States
Console.WriteLine(city.City.Name);    // for example, Minneapolis