Permanent ID for OSM

 This is an unofficial proposal for a "OSM permanent ID" (osm_pid) for OpenStreetMap (OSM). 
 See here for a more well known place for discussions. 

Goals and Requirements

The goal is to get an opaque (eventually fixed) length ASCII string for an OSM id.

That are the design considerations:

• The OSM id alone is not stable enough (as probably most agree); and it can represent many concepts (and that's by design in OSM).
• The version no. of the object is needed which makes clear which tags are (or have been) referred to.
• Coordinates are needed, because a change of the way and area geometries does not increment the version number.

Status of OSM id

One can use OSM id nevertheless (at own risk)! Many variants are known:

As is with OSM id (bigint) and a code for Node, Way, Relation e.g. in front (e.g. way/417258377). Currently many applications depend on plain osm_id, eventually preceeded by node,way,relation (or N/W/R), like theses web applications (given example of "Denner Hombrechtikon" https://www.openstreetmap.org/node/6313169265):

• Qwant Maps: Example Denner Hombrechtikon https://www.qwant.com/maps/place/osm:node:6313169265@Denner#map=18.00/47.2519793/8.7681836
• Castle Map: Example Schloss Rapperswil https://castle-map.infs.ch/#46.805,8.205,8z,W417258377
• Mapbox Vector Tiles: rely also on OSM id plus Node, Way, Relation: see below.

Another adoption of osm_id with enhanced type space (length) properties is to convert it to a single big integer: It's possible to encode the type (Node, Way, Relation) into the OSM id as a single integer (64 bit). (Source: Mapbox, see [1]). Example: "Schloss Kyburg" is a relation with id 1169711, so it becomes 11697114.

 for Nodes: osm_id = <node id> × 10  (eg. 123 → 1230), 
 for Ways: osm_id = (<way id> × 10) + 1  (eg. 123 → 1231), 
 for Relations: osm_id = (<relation id> × 10) + 4  (eg. 123 → 1234).

Recommendations

These is what we currently recommend, depending on the setting (see explanations below):

1. OSM id with Node-Way-Relation code (at own risk). Example 'relation/1169711'.
2. Wikidata QID with OSM backlink. Example 'Q573643'.
3. Overpass Permanent ID with objekt-group-specific ID. Example '[out:custom];rel[wikidata=Q573643];out;'
4. OSM Permanent ID with geo URL. Example 'geo:47.4584,8.74343?q=relation/1169711#5'.

OSM Permanent ID with geo URL

A stable Permanent ID could have the following form using the international 'geo' URI scheme (variable length to a maximum of currently 42 chars):

 'geo:'[+|-]<lon>[+|-]<lat>'?q='[node|way|relation]'/'<osm_id>#<osm_version>

where:

• the form 'relation/1169711' is the same as e.g. Overpass JSON output produces as @id.
• osm_id an unsigned big integer ("digits").
• osm_version is an unsigned integer with a hash in front.
• coordinates (lat/lon) are signed floats (always showing the +/- sign), with a maximum of 6 digits. In case of a line (linestring) or an area (multipolygon relation) geometries, the coordinates taken into account are the lat/lon minimum of the geometry.

Example: "Schloss Kyburg" (Castle Kyburg) has relation 1169711, version #5 at coordinates 47.45835, 8.74375 which becomes following OSM Permanent ID (osm_pid):

 osm_pid = geo:47.45835,8.74375?q=relation/1169711#5

There's a implementation by Mangrove.reviews with some slightly different parameters q and u (for 'uncertainty' in meters).

Examples:

• Castle Kyburg: 'geo:47.45835,8.74375?q=Kyburg&u=30' => [2]
• Supermarket Denner Partner, Hombrechtikon, https://www.openstreetmap.org/node/6313169265: 'geo:47.2520925,8.7683656?q=DennerPartner&u=30' => [3]

 Note: The geo URI looks like a web link (URL). Unfortunately almost no browser supports this URI 'out of the box', only Android systems.

OSM Permanent ID Service

In order to be really useful, a service should be implemented, which returns most recent object given a possibly old Permanent ID if an object has been changed; thus having another Permanent ID where any of it's parts may have changed (most probably just the version no.). Such a service must have access to the fully planet including the history and it must be reliable and responsive.

Alternatives

 See https://wiki.openstreetmap.org/wiki/Permanent_ID for a more official state of discussions. 

Wikidata QID with OSM backlink

If all objects in question are allowed to become a Wikidata (WD) object, add the Wikidata QID with key 'wikidata' to the OSM object. This one-way link from OSM to Wikidata then can be turned into a two way relationship using database techniques of JOINs. On the other hand you can add to a Wikidata object the coordinates (P625) and the OSM relation id (P402). Many mashups of OSM, Wikidata and Wikipedia use this solution, like the castle dossier (Burgen-Dossier) and others.

Example for Castle Kyburg: Q573643.

 Warning: Don't shoehorn all OSM objects to relations just because Wikidata only knows OSM relation id (and no node/way id)!

Overpass' Permanent ID

The Permanent_ID from Overpass is a solution where one expects to see the details (= "Link to Browse Object") and which relies purely on (non-geographic) tags: https://wiki.openstreetmap.org/wiki/Overpass_API/Permanent_ID

Example for Castle Kyburg: '[out:custom];rel[wikidata=Q573643];out;' => Q573643

Others

• OpenLR (Location Referencing) - a free spec. by TomTom for linear geometries like streets [4].
• The geographical object IDs from authorities like Ordnance Survey UK or Swisstopo CH.