Discardable tags are tags that the OpenStreetMap community have found not to be useful; either changes to OSM’s API or licensing have made them redundant or they were added in an import and later found not to be useful.
Editors may remove these tags automatically when they save new versions of nodes, ways or relations. Editors may remove such tags silently, without ever notifying user that tag was present but in addition to other modification edit also removes such tags. It differs from handling of deprecated tags where editors notify user about possibility to change tag, made change is not hidden from user and tag may be not just deleted but replaced by a new one.
Each editor has its own list of automatically discarded tags.
- Discardable tags in iD, Vespucci is using the same list
- Discardable tags in JOSM — under “getDiscardableKeys()”
- Discardable tags in Potlatch — under “var discardTags:Array”
- StreetComplete has no automatically discardable tags
To make tag discardable one needs to suggest this change to developers of editors - note that it requires explanation why given tag is so useless that it can be hidden from users and silently deleted.
Comparison with automated edits
Discardable tags are a way to remove unwanted tags from OSM database. Alternative method to do the same is to run an automated edits removing them (note Automated Edits code of conduct). The end result is the same, offending tag is gone from OSM database. Removing with discardable tags is significantly slower and tag stays in OSM database for decades, but it is mostly hidden from mappers as editors are not displaying it. It also results in a slightly more confusing changesets as changes made by mappers and changes silently made by editor are mixed. On the other hand running a proper automated edit requires more effort and requires making additional edits adding entries in history of objects and changing their data of the latest edit.
- Deprecated features - tags that are not silently removed but are suggested to be replaced by an alternative tagging schemes - for example waterway=wadi of shop=underwear
- https://lists.openstreetmap.org/pipermail/talk/2019-March/082329.html - see the end "You don't need to do anything separate for Vespucci, simply make a PR against https://github.com/openstreetmap/iD/blob/develop/data/discarded.json"