Nominatim

Nominatim is a geocoding search engine for OpenStreetMap data. It provides forward geocoding, which converts place names or addresses into geographic coordinates, and reverse geocoding, which retrieves an address and location information from coordinates. The project is developed and maintained by the OpenStreetMap community and can be run as a local service or accessed through public instances.

Nominatim relies on OpenStreetMap as its data source and is designed to keep its index in sync with OSM exports. The typical backend stack uses PostgreSQL with PostGIS, augmented by a specialized indexing system to support fast searches across names, addresses, and geographic features. Data updates come from regular OSM data releases, allowing the service to reflect changes in the map data.

The service offers a RESTful API for both forward and reverse geocoding. API responses can be returned in JSON or XML and include fields such as display_name, latitude, longitude, and address details. Common query parameters include q for the search string, format for response format, addressdetails to request structured address data, limit to cap results, and filters like countrycodes or viewbox. Public instances exist but impose rate limits and usage guidelines; heavy or automated use is advised to run a local instance or obtain permission.

Nominatim is open-source software released under the GNU Affero General Public License. It plays a central role in many mapping and location-based applications by providing place-name and address lookup tied directly to OpenStreetMap data, enabling users to find locations, verify addresses, and integrate geocoding into various services.