Per @Pnorman, we are using this default style with osm2pgsql, which we should alter to add the wikidataid. See also our current install script

Querying all readable columns from the polygon table using the new wikidata id index (above).
Note that we check that tags contains 'wikidata' key AND it is equal to our value. Without this, our index is not being used, and it does full table scan instead.

SELECT
osm_id,access,"addr:housename","addr:housenumber","addr:interpolation",admin_level,aerialway,aeroway,amenity,area,barrier,bicycle,brand,bridge,boundary,building,construction,covered,culvert,cutting,denomination,disused,embankment,foot,"generator:source",harbour,highway,historic,horse,intermittent,junction,landuse,layer,leisure,lock,man_made,military,motorcar,name,"natural",office,oneway,operator,place,population,power,power_source,public_transport,railway,ref,religion,route,service,shop,sport,surface,toll,tourism,"tower:type",tracktype,tunnel,water,waterway,wetland,width,wood,z_order,way_area, tags
FROM planet_osm_polygon
WHERE tags ? 'wikidata' and tags->'wikidata' = 'Q1166';

I found the following columns interesting: admin_level, boundary, name, ref, z_order, way_area. I wonder if we could use the way_area to figure out the best way simplification? Reading relevant literature.

Some interesting results searching for (tags->'wikidata' IN ('Q1166', 'Q16', 'Q30', 'Q46', 'Q2', 'Q98')) (Michigan, Canada, USA, Europe, Earth, Pacific Ocean): found 1 Michigan, 3 Canadas, and about 55 USAs. No other items were given (I was hoping for Europe)

Simplification notes from @Pnorman moved to T138154#2392658

This service is now implemented and can be enabled as part of Maps (Kartotherian) by adding this config block as described in the README:

Make sure to create OSM index as specified in the description above

geoshapes:
  host: localhost
  database: gis
  table: planet_osm_polygon
  user: ...
  password: ...

TODO: decide on what simplification formula to use