Downloading OpenStreetMap (OSM) Data for GIS

OpenStreetMap (OSM) is the Wikipedia of maps. It is a massive, open-source database of global spatial data maintained by millions of volunteers. It contains incredibly detailed information on roads, buildings, land use, and points of interest.

However, downloading data from OSM is different from downloading a standard Shapefile. This guide explains how to extract OSM data for your GIS projects.

The OSM Data Model

OSM uses a topological data structure consisting of three primitive types:

• Nodes: A single point with a latitude and longitude.
• Ways: An ordered list of nodes (used for roads, rivers, or polygon outlines).
• Relations: A group of nodes, ways, or other relations (used for complex features like bus routes or multipolygons).

Because of this model, you cannot simply download a single file and load it into ArcGIS or QGIS without some processing.

Method 1: Geofabrik (Large Extracts)

If you need data for an entire country, state, or continent, Geofabrik is the best source.

1. Go to download.geofabrik.de.
2. Navigate to your region of interest.
3. Download the .shp.zip file (which contains pre-converted Shapefiles for common layers like roads and buildings).
4. Extract the ZIP and load the Shapefiles into your GIS software.

Method 2: Overpass Turbo (Custom Extracts)

If you only need a specific feature (e.g., all cafes in a city), use Overpass Turbo.

1. Go to overpass-turbo.eu.
2. Pan and zoom the map to your area of interest.
3. Click "Wizard" and type what you are looking for (e.g., "cafes in London").
4. Click "Build and Run Query".
5. Once the data appears, click "Export" and choose "Download as GeoJSON".

Method 3: QGIS OSM Tools

If you use QGIS, you can download OSM data directly.

1. Install the "QuickOSM" plugin.
2. Open QuickOSM from the Vector menu.
3. Enter your query (e.g., Key: amenity, Value: restaurant) and your location (e.g., a city name).
4. Click Run Query. QuickOSM will download the data and add it directly to your QGIS project.

The OSM License (ODbL)

OSM data is licensed under the Open Database License (ODbL). This means you can use it for free, but if you publicly distribute a modified version of the database, you must also share it under the ODbL. You must also provide attribution to "© OpenStreetMap contributors".

Summary

OpenStreetMap is an invaluable source of free geospatial data. By using Geofabrik for bulk data or Overpass Turbo for specific features, you can easily integrate OSM data into your GIS workflows.