I've refined my first efforts to now highlight where you are in the tree. The trees on display here now show the new look.Basically I've abandoned image maps as they don't allow me to highlight the part of the tree being selected. After some fussing I switched to using HTML DIVs, which sit on top of the image. This took a little while to get working, CSS and DIV placement drives me nuts.

OK, time to put my money where my mouth is. Here's a first stab at displaying big trees in a browser. Not terribly sophisticated, but reasonably fast. Take a look at Big Trees. Approach Given a tree I simply draw it in a predetermined area (in these examples 400 x 600 pixels). If there are more leaves than can be drawn without overlapping I simply cull the leaf labels.