Proposal

In pageprops, store map-related geojson data as an object:

{
  "groups": {
    "groupID1": [ {...geojson1...} ],
    "groupID2": [ {...geojson2...},  {...geojson3...} ],
    ...
  },
  "maps": {
    "hash1": [ "groupID1" ],
    "hash2": [ "groupID1", "groupID2" ],
    ...
  }
}

In the above, "hash2" is calculated by first concatenating into the same array all groups and their content, converting to a string, running a hash function.

hash( JSON.stringify( [ "groupID1", {...geojson1...}, "groupID2", {...geojson2...},  {...geojson3...} ] ))

URL to get a static map - params: style, zoom, latitude, longitude, width x height. The hash could be made shorter to make it a bit less scary, e.g. first 4 hash symbols. Together with the page title, this should be more than enough to identify the map's data.

https://maps.wikimedia.org/img/osm-intl,15,37.8040,-122.4098,1000x1000.png?site=en.wikipedia.org&title=My_page&id=hash1

Alternatively, we could expose static service via restbase, so that wiki can load static map from the same domain, without creating a separate https connection:

https://en.wikipedia.org/api/rest_v1/page/map/png/My_page/hash1/osm-intl,15,37.8040,-122.4098,1000x1000.png

Can we get a little bit more context here? This smells like something that we can achieve using the EventBus and the change-propagation service we have in production, but there are too many missing details (like, what is this about, what do you want to achieve, etc etc)

We'll need to add revision id into play for support of past revisions. The API would retrieve groups for current revid from page_props while for past revisions it would have to rely on parser output.

I would prefer to keep it simple without revids, until we implement T119043

Do you want/need to pre-generate the maps or render them on demand? Would this flow describe what you want to achieve: page edit -> get page-props -> render the map -> store it now, serve later ?

Done:
http://maps.wikimedia.org/img/osm-intl,1,0,0,1000x1000.png?domain=www.mediawiki.org&title=Help:Extension:Kartographer&groups=_925bf4f20f98fdda374476b902f702d080492748