If coordinates and zoom are not specified for maps with geomasks, the static thumbmail map seems to be generated all zoomed out (zoom=0) which makes the thumbmail map pretty useless. It works fine for the same maps with geoshapes instead of geomasks. Please see examples in my Wikipedia sandbox at User:Dipsacus fullonum/sandbox/geoshape. Is this a known issue and is there a workaround?
Topic on Help talk:Extension:Kartographer
That's a really good example page, thanks for that! The reason for this behavior is how masks are implemented: as inverted shapes. A mask is just a shape that covers the entire world – with a hole. That's what the automatic zoom feature sees and why it shows the entire world. While it might be possible to improve the automatic zoom to understand this better I don't think anyone can assign resources to this at the moment.
@Thiemo Kreuz (WMDE) This is a regression due to a rewrite that happened in 2022 and didn't account for this situation. The ticket is phab:T305121
@Thiemo Kreuz (WMDE) @TheDJ Such a shame that this isn't working, there are multiple examples on enwiki (collapsed boxes here e.g.) that are showing this bug. But why Dipsacus' examples 1, 2 & 4 seem OK while I'm editing their sandbox (code) and previewing either in real time or by pressing the preview button? And why are they not working in a completely different way when editing in VisualEditor?
The maps are generally rendered in two surprisingly different ways: Either as a dynamic map in your browser or as a static image. The wikitext preview works because it is done in your browser and doesn't involve the broken code mentioned in phab:T305121.
The issue we see in VisualEditor is very closely related, if not the same. VisualEditor generally has a very hard time doing anything with non-trivial maps.