Wikidata, as a project derived from Wikipedia, could be viewed as a crowdsourced database of VGI (Volunteered Geographical Information), of course less structured than OpenStreetMap spatially but at least comparable: we think that a cross-reference could be worthwhile for both projects. This work has already started from some years ago with the wikipedia tag (notably the WIWOSM project, and in Italy wtosm) but now the focus seems to be moving towards the use of Wikidata instead of Wikipedia.
In this post I would like to introduce our experiment in this direction, powered by the resources we have as a chapter of both the OSMF and the WMF.
We started from an existing OSM database replicated every half hour through osmosis, where all the tags are dumped in an hstore column and we added a table called wikidata and a view which gathers existing elements tagged with the wikidata key (UNION of nodes, ways and relations).
The wikidata table is populated by a script which parses the weekly Wikidata dump (~10 GB gzipped line delimited json): we get only the elements having a claim with the P625 property (an element with at least a coordinate) and we take only the ones in Italy (a "rough" point in polygon test). The objects are then saved with the most precise coordinate available, their id and a label (italian, english, serbo-croatian or the first available).
Why serbo-croatian you may ask? We noticed that the Wikipedia editors created a lot of stubs from Geonames which went to generate new Wikidata items having only the label in the sh iso code :-)
Now we have our brand new table and we can create our service: a map showing all the Wikidata elements colored by their OSM status. Green if already matched, Red if it’s an element which can't appear in OSM (an historical battle or structure for example), Grey if they still need to be processed. Each marker has its popup, linking to the object on Wikidata (and on OSM), the wikidata tag to copy, and two buttons: one to mark the object as non-mappable, the other to mark it temporarily done (it would -hopefully- become green on the next run).
The service is live at http://osmit3.wmflabs.org/wikidata/ and covers Italy.