Probably a stupid question, but:
Would it be acceptable to insert not administratively defined macroregions encompassing more than one country such as Sahel, Sahara, Amazonas directly under the continent level?
This is fine. In order to include it in a hierarchy you can use the menu links 'part-of' to define the continet it belongs to and the menu link 'contains' to define the countries it contains.
Thanks a lot.
This would make the existing, geographically misplaced Sahel region within Chad obsolete, right?
And, since this form of hierarchy does not seem to show up in the geotree, is there any place where it is either detailed to the wider public or represented graphically?