You can use the Overpass API to download filtered data: http://wiki.openstreetmap.org/wiki/Overpass_API/Language_Guide
This is what an Overpass API call might look like:
You will get a file named
interpreter; rename it to
Load the data with
Vector -> Openstreetmap -> Import topology from XML
interpreter.osm file. The data will be stored in a spatialite database called
Don't panic if you see nothing yet, choose
Vector -> Openstreetmap -> Export Topology to Spatialite
interpreter.osm.db database, selecting Polylines in a first run, and Polygons in a second one (see screenshot). You should click
Load from DB and choose
name to get the name tag as well.
Then you can add an Openstreetmap background with the OpenLayers plugin, showing you where the zones are placedd.
The next step would be to close the boundaries to polygons. A simple
Lines to Polygons action will not give good results, so you have to do a little handwork redrawing them in a polygon layer (or use JOSM for that, see below).
Due to the non-standarized data structure of OSM, you might as well look out for:
If you prefer JOSM, look up the existing data on this page:
Click on the relation number, then copy the relation number from the html page.
In JOSM, File - Download Object, Object type : relation, and check Download relation objects. The relation ID should be preset already.
Save as .osm, and proceed in QGIS as mentioned above.
If you promise not to upload on leaving JOSM, you can even search for the missing bit in the boundary, connect all ways and copy the relation tags to the resulting single line.
You have to keep an eye on every boundary to avoid roundabouts and ways without continuation. In Magdeburg and Neu-Ulm, they simply added all streets in the zone to the relation. So you have to draw the border yourself. And some towns have several polygons, because certain motorways are excluded from the zone.
With the improved JOSM data, an import into QGIS as polygon (as described above) will work:
Searching for names like "Umweltzone" eventually contains the zone for Munich as well:
A closed line only tagged with