A few users on the Wikimedia Commons have been discussing how to cross-reference Commons multimedia with OSM features. For example, a photograph on the Commons may depict one or more relation, way, or node recorded in the OSM Planet. These features can be referenced from the Commons item page, and automatically link to the OSM feature. If the cross-reference contains machine-readable information, services may be built on top of the linked open data.
Thank you for the link. The method seems very similar to the goal of Wikimedia Commons cross-referencing.
Is it possible to simultaneously tag several OSM features? E.g. can I select several map features and add a ‘wikimedia=ID’ attribute to all selected features? This would be helpful, as some media depict several OSM features. E.g. streets, street segments, sidewalks, buildings, benches, fountains, etc.
The problem with permanent links between OSM and external databases is that OSM does not offer any stable IDs. That doesn’t stop some projects from using these IDs as if they were stable (e.g. Flickr, as well as the hastily conceived “OSM Relation” property in Wikidata), but ultimately that’s a not a proper solution. If you reference a specific version together with the id, that is pretty stable, but doesn’t allow you to access the current representation of that feature.
Therefore, we sometimes use the opposite direction: Adding tags into OSM which reference external “IDs”. This is the case with the wikipedia=* tags used by WIWOSM, where the Wikipedia page title, along with the language version, is treated as an ID. Although that information isn’t completely stable either, it is at least a step in the right direction. Likewise, we have a relatively new wikidata=* tag, where the values should hopefully be even more stable.
The downside of this solution is that this only works well because there is at most one Wikidata item (or, equivalently, one set of Wikipedia pages) per OSM element; and at least currently only for the relatively small subset of elements considered “notable” by Wikipedia/Wikidata. While it would be possible to add a tag to multiple elements at once with the more advanced editors such as JOSM - to answer the question from your second post - it might not be a good idea: Adding a large number of external IDs to even trivial OSM objects, as your idea implies, would most likely be very controversial because of the impact on everyday OSM editing.