Swiss Postal Codes

This comparision lists the value of "postal_code" on the municipality admin boundaries and the corresponding official postal code polygons http://www.cadastre.ch/internet/cadastre/de/home/products/plz/data.html. The values for the OSM postal_code is the PLZ4 value, the official polygons have the PLZ6 one (note the PLZ6 is not used for addressing, always use the PLZ4).

Besides intentional differences in the post code polygons to the admin boundaries see for example http://qa.poole.ch/plz.html?osm_id=-1682103, there are a number of small errors in the official polygons that require some heuristics to determine which post codes are actually in use in a specific municipality. As with all such herustics there may be errors and the results should be checked against reality before any real use.

Switzerland has essentially three different formal concepts of "places" in the sense of human settlements: the municipalities (boundaries imported and maintained in OSM), places ("Orte", available as place nodes in OSM) and postal places ("Ortschaften"). In the case when all three are the same the situation is simple and adding the PLZ4 to the boundary relation can make sense, however this is only the case in a minority of situations. A sensible solution for the complex cases would seem to be to add the PLZ4 to buildings/entrances as the addr:postcode value.

Updated - 2013-5-25