I think the main source of ambiguity is the open-gis tag which seems more often to be used for the Open Geospatial Consortium but sometimes for Open Source GIS.
To disambiguate it and tidy up the other mentioned tags into something easier to work with I am going to suggest:
- Merging open-source into a new tag called open-source-gis which would leave open-source as a synonym. There may be some questions here that are about Open Source software other than Open Source GIS but I think they are few and far between, and will only be peripheral to the questions they are placed on. For example, a Python question may have been tagged open-source but more likely it is tagged python anyway. If the focus of a question is about Open Source software other than Open Source GIS it is probably off topic anyway.
- Retagging any open-gis questions about Open Source GIS to open-source-gis - I think there is only one
- Merging any remaining open-gis questions into ogc which would leave open-gis as a synonym.