Map Display

I am interesting in using VisAD to display a map of a river system. For
starters, I simply want a map of nodes (circles) and paths (line
segments connecting nodes). I assume this is doable, but I am not sure
where to begin as I'm just getting up to speed with VisAD. In
particular, how do I go about rendering a circle given coordinates for
its center and given its radius? I would implement this via Java2D which
supports geometric shapes, but how do I drill down to this Java2D
feature from within VisAD? Any advice would be appreceated.

Thanks, John

-- 
John B. Parrish, Ph.D.
1165 Elderberry Circle
Folsom, CA 95630
Office: 916-983-6267
Fax:    916-983-6281
email:  parrish@xxxxxx