OpenStreetMap
OpenStreetMap (OSM) is often described as the Wikipedia of maps. Since 2004 volunteers have mapped the world by hand and from aerial imagery, tagging every feature with structured attributes. The result is a rich, freely licensed dataset covering streets, addresses, shops, natural features, administrative boundaries, and public transport across the globe.
You can grab the full planet dump or country and region extracts from mirrors such as Geofabrik. The data comes in OSM XML and the more compact PBF (Protocol Buffer Format) binary, and tools like osmium and Osmosis help you filter and convert it. A live editing API and read-only Overpass API let you query features directly.
For RAG, OSM is a strong source of place names, addresses, and points of interest that you can turn into a knowledge base for location-aware questions. It underpins countless mapping products and feeds Overture Maps, which harmonises OSM with data from other contributors.
Related sources
GeoNames
A geographical database of more than 11 million place names, each with coordinates, population, elevation, and administrative divisions, covering every country. It works well as a gazetteer for resolving place names to locations.
Natural Earth
A public domain map dataset built for cartography, offered at three scales: 1:10m, 1:50m, and 1:110m. It bundles cultural data (borders, cities, roads), physical data (coastlines, rivers, lakes), and raster imagery, all ready to drop into a map.
Overture Maps Foundation
An open map data project run under the Linux Foundation by a group of industry members. It combines and harmonises data from OpenStreetMap, Microsoft, Meta, and others into consistent, interoperable map layers you can build on freely.