Nominatim

Nominatim is an open-source geocoding engine that searches OpenStreetMap (OSM) data by name and address and generates addresses from OSM objects (reverse geocoding). It provides both a REST API and a Python library surface for embedding search functionality and supports structured queries and configurable result ranking.

Key Features

• Forward geocoding (free-form and structured queries) and reverse geocoding for latitude/longitude pairs
• REST API and Python library for programmatic use, plus a web UI for manual lookups
• Import and update tooling for OSM data (osm2pgsql-based workflows and minutely/osc updates)
• Configurable tokenizers, ranking, and importance scoring (supports external data like TIGER/Wikidata for ranking)
• Scalable installs: from single-city setups to full-planet imports with tuned PostgreSQL/PostGIS databases
• Customization hooks for import styles, address handling, and API result formatting

Use Cases

• Powering a site or app search box to resolve user-entered addresses and place names
• Reverse-geocoding GPS traces to human-readable addresses for mapping or logging
• Bulk-geocoding address lists as part of data integrations or ETL pipelines

Limitations and Considerations

• Full-planet imports are resource-intensive (large RAM/disk requirements and long import times); adequate hardware and PostgreSQL tuning are required
• Relies on PostgreSQL/PostGIS and external import tools; version compatibility (PostgreSQL/PostGIS/osm2pgsql) should be verified before install
• Public instance enforces usage policy and rate limits; high-volume use requires a self-hosted instance or commercial provider

Nominatim is a mature, OSM-native geocoder used by the OpenStreetMap project itself. It is suitable for projects that need control over geocoding data, custom ranking, or on-premises operation, provided the deployer accounts for its operational requirements.