Nice thought, that. Couldn't we also have 1-place gismu as points, 2-place gismu as lines, and 3-place gismu as triangles? --And
Erm, what would be the point? Of any of this? Could we visualize them fitting together somehow? What's on the boundary of cakla and stizu or carvi and lanme? How would this be worth working on?
--The point being, getting ahold of that other hemisphere would make learning the meaning and use of the sumti-places a whole lot easier. Pictures plus words equal the Art of Memory.
So picture them as 3-wheels, 4-wheels, and 5-wheels (rings of 3, 4, or 5 nodes, connected to one central hub) for those that have enough places, and for the smaller ones, well, fake it (line segments, simple rooted trees). You can orient them in your mind so you can associate each place with a location, just as with a tetrahedron. And it's flexible enough to handle fu'ivla with more than 5 places too.
- If I understand you correctly, I think you're missing the point. If you conceptualize selbri as relationships among the sumti, there is no central hub; there is only the n-way relationship, which, by the original suggestion, is visualized as a collection of pairwise relations between the sumti. And
(I'm glad this notion is being developed some--perhaps a Lojban primer could have pictures of what's at some of the sumti positions for each of the gismu diagrammed...)