Why the rosettes image may not be a map at all

[MarcoP]

I wonder whether it would make sense to look for parallels for these buildings on things like portolan charts? Those are surely some of the closest things we know to this foldout...

Hi Koen,
I think the most perspicuous features of portolan charts is their relatively accurate representation of the shape and accidents of coast lines and the extensive use of "windrose lines". They seem to me to be "more scientific" than earlier medieval maps.

On the other hand, the Rosettes foldout is a neatly symmetrical diagram featuring a number of apparently symbolic elements. It is obviously based on circles, which appear in numberless medieval diagrams (rotae) but typically not in portolan charts. For these reasons, I see it as more "medieval" and "abstract" than portolan charts and I also think it possible that, as the thread title says, it "may not be a map at all".

Could you please list a few traits typical of portalan charts (i.e. absent in other medieval charts) that make them "some of the closest things we know to this foldout"?