Using OpenStreetMap data almost always requires filtering for thematic extracts. Overpass API is a web service for this purpose, available at overpass-api.de. Its source code is licensed under AGPL.

The open data project OpenStreetMap aims at creating a geographic database of the entire world, i.e. collecting the data necessary to make any map of what is on the ground. Starting in 2004, it has now grown to more than a million registered mappers. In most places details are mapped including each footpath. In some places even streetlamps, trees, wastebaskets, and similar things are mapped.

Overpass API allows you to extract data by geographic search criteria, by subject, by structual properties or an arbitrary combination of them. In this way you can realize an always up-to-date data overlay on a slippy map, a desktop data browser, conveniently pull data from OpenStreetMap into QGIS, do quality assurance or a lot of other things.

In this talk I will present Overpass API by the above mentioned example use cases. Furthermore, I will give a short overview over the components and the query language. This gives you a starting point to integrate OpenStreetMap data into your application of choice.