Beautiful visualization. One thing missing though is a color-scale for age. Difficult to tell what color represents older vs newer and what are the magnitudes of the differences in age.
Thanks, good point, the colour-key box should change when the "age" colour scheme is selected. For now: the newest papers are red and oldest papers are gray, and, as you may have noticed, the gradient from gray to red is 1-1 but not linear with age. For a bit more of an explanation see this post: http://blog.paperscape.org/?p=60
