There is now a new Wikidata property for Carthalia pages:

https://www.wikidata.org/wiki/Property:P5652

It's fun to play around with the possibilities of Wikidata. Here's a world map of theatres on Carthalia:

https://tinyurl.com/ya9x4n6n

It will not be complete before I haven't entered all theatres with postcards in my collection into Wikidata - however, there are already around 1.900 items there that feature the Carthalia ID. Furthermore, not all Wikidata items on theatres have geographical coordinates. I will try to add those, too.