Geocoding

The problem looks trivial and is not. Addresses are written differently by everyone, arrive incomplete, are misspelled, get reused between towns, and sometimes exist in no register at all. A geocoder therefore has to normalise the text, guess which part is the street and which the locality, and return an answer with a confidence level rather than a correct one. Precision ranges from an exact building to "somewhere in this postcode", which rarely shows in the API response unless you read it carefully.

Reverse geocoding — from a GPS fix to the nearest address — powers everything from delivery apps to the place tag on a photo. Open alternatives built on OpenStreetMap exist, such as Nominatim and Photon, but the terms differ sharply from the commercial ones: nearly every large provider forbids storing the results or displaying them on any map but their own.