Jerry,

>Has anyone looked at hyperbolic trees?  I find them hard to explain, but
>very easy to grasp once you play with them.

I looked over that pretty thoroughly. There is an article explaining the
underlying principle in SIGCHI '95 called  'A Focus+Context Technique Based
on Hyperbolic Geometry for Visualizing Large Hierarchies' by Lamping,Rao and
Pirolli pp. 401.

There are some interesting applications, one example is a web site
navigation tool. Basically the hyperbolic tree is built from all of the
navigable nodes at a web site, and then the user can navigate the web site
based on this tree, rather than following hyperlinks embedded in each page.

This is an innovative solution to the problem of traversing large
hierarchies using limited screen space. Inxight basically wants US $10,000
for a development version if you want to develop with it for a product. Oh,
and they have nice 4 color brochures too !!!

Personally, I think it looks pretty cool, but I have not figured out how
useful it is. The applications that I have seen so far provide a different
way to look at a namespace, but I do not think it provides any extra useful
information.

For example, in the Louvre demo you could see how all of the nodes of the
tree were related, but those relations did not give you any more insight
into what each node of the tree contains. The node contents tend to be what
I am interested in, not the structure of the tree, and it is not quite clear
how I search thru one of these trees. I think perspective walls and document
lenses are more useful for looking thru large amounts of data in this
context.

jb