GIS is only as good as its data, and the best data is free: OpenStreetMap, Natural Earth, and a handful of government sources cover the whole planet, from country boundaries to individual buildings. The challenge is knowing where to look and what to trust. This guide lists the free sources that matter and how to use them.

OpenStreetMap: The People's Map

OpenStreetMap is the largest free mapping dataset in the world, built by volunteers, covering roads, buildings, land use, and points of interest for almost every inhabited place. Download it from Geofabrik, which offers regional extracts, or query it with Overpass Turbo for specific features. The data is detailed in cities and thinner in rural areas, and quality varies, but for most projects it is the first source to check. Always credit OpenStreetMap and its contributors when you use it.

Natural Earth: The Cartographer's Choice

Natural Earth provides free vector and raster data designed for making beautiful maps: country boundaries, populated places, rivers, and shaded relief, all in public domain. It is the standard source for small-scale world and regional maps, and it is what most cartographers reach for first. The data is generalised for display rather than analysis, so do not use it for precise measurements, but for a map that needs to look good, it is unbeatable.

Government Sources: The Authoritative Data

Most governments publish free geospatial data: the USGS offers elevation, hydrography and land cover for the United States, the European Union's INSPIRE portal aggregates data from member states, and the UK's Ordnance Survey offers open data through OS OpenData. Government data is authoritative and well documented, but it varies in format and licence by country, so check both before you download. For official boundaries and administrative areas, government sources are the only correct choice.

Specialist Sources for Specific Needs

For elevation, use the SRTM or ALOS global datasets, both free and covering most of the planet. For land cover, use ESA WorldCover or the Copernicus Global Land Service. For population, use WorldPop or the Gridded Population of the World. For coastlines and bathymetry, use GEBCO. Each specialist source is maintained by experts in its field, and the documentation tells you exactly what the data means and how accurate it is.

Checking Quality Before You Use Data

Before you build a project on free data, check its age, its resolution, and its licence. Old data can be dangerously out of date, especially for roads and land use in fast-growing areas. Check the metadata for the collection date and the known issues, and compare the data against a satellite basemap to spot obvious errors. Free data is not always good data, but the best free sources document their limitations honestly, and that honesty is what makes them trustworthy.

Open Data and the GIS Community

The free GIS data ecosystem depends on contributors: OpenStreetMap is built by volunteers, Natural Earth is maintained by a small team, and the government datasets are funded by taxpayers. The data is free, but it is not free to produce, and the community needs contributors. Add a road to OpenStreetMap, fix an error, or share a dataset you created: the contribution is small, but the impact is large. The open data movement works because people contribute, and the beginner who contributes becomes part of the community.

Key Takeaways

- OpenStreetMap is the largest free mapping dataset, built by volunteers - Natural Earth is the standard for beautiful small-scale maps - Government sources are authoritative for boundaries and administrative areas - Check age, resolution and licence before building on free data

Frequently Asked Questions

Where can I download free GIS data? OpenStreetMap from Geofabrik for detailed features, Natural Earth for cartography, and government portals like the USGS and INSPIRE for authoritative data.

The best GIS data is free, but it varies in quality. Check the source, read the metadata, and compare it against a basemap before you trust it.