Viewing missing methods/software

The key interesting thing about TreeTapper for me is the ability to find missing methods or software. Any list of software and methods will tell you what's available (and isn't trivial to make), but for developers, finding what doesn't exist yet is key. At first, I was just doing a typical treeview (not in the phylogeny sense, but in the nested series of folders sense):

I started adding the beginnings of  bar plots (the red squares above) to show the number of techniques/question available for each topic. The problem with this is that it's very hard to get a quick overview of what's missing: a user has to drill down into each section and remember what's there (sensible display of some of this in with bar plots might help, but it's still not great).  But thinking about it, what would be good to show is an actual tree: for a given starting point (such as a topic: speciation rate), and then all possible descendants (such as all possible questions for this topic). Those descendants available in methods/software get one branch color (say, black), those not get another branch color (gray) [though it might be good to distinguish those present in methods but not software]. Here's a hand-drawn example for the basic idea:

And with colors and labels:

Under this approach, it's easy to distinguish areas with methods/software available (black/solid) from those lacking methods or software (gray/translucent). In the example above, the central dot represents a topic, the first circle represents questions, the second circle criteria, the third perhaps character type, etc. Derrick Zwickl had the good suggestion to allow users to set the order in which options are plotted; I'd also like to allow users to fix certain values (only look for missing methods under a likelihood criterion, for example).

The problem is that this is just a dummy layout, drawn in Apple Keynote, not actually a working image. The question becomes how to make it. I'm thinking of first having a YUI table with the various options to plot (criterion, method, character types, etc.), and then having a second table (or allowing ranking on the first table) where users can drag the options to plot them on the tree in the given order (see an example of something grossly similar here). One problem may be writing the logic to be able to look at all the options for variable Y when it descends from variable X, including which ones are and are not available, when what X and Y are is up to the user (perhaps comparing a cross-join and a left-join postgres table, or something like that, would be the key). Another question is how to actually generate the plot. There are  various Java libraries for interactive data plotting (the first thing I would try if I went this route would be generating an interface with Processing), but many of them failed when I tried them with the most recent version of Mac's Safari, and Java online (and on the desktop, too) always feels a bit clunky to me. There are various ways to make plots on the web (such as Google Charts and Yahoo Charts), but they only have a few mouseover options. I'm actually thinking of using the Google Maps API for this. Using that, plotting points, lines, and areas is now possible, and users can get information on nodes by clicking on them and one can add various javascript functions called onmouseover, onclick, etc. Users will be able to zoom in on parts of a tree. Finally, one can add custom map tiles to replace the Google tiles; in my case, I'd just have a white background, and do all the plotting with polylines and the like. This sort of use of Google Maps been done before; I remember Katy Böhner mentioning this in a talk (though I couldn't find anything on her lab's website), and there are other examples online. 

Well, we'll see how it goes. As with all posts, please feel free to make suggestions in the comments.