Data presentation

Treemaps are space-filling approach to showing hierachies in wich the rectangular screen space is divided into regions, and then each region is divided again for each level in the hierarchie. The advantage of this representations is that, by construction, they make efficient use of space. As a result, they can legibly display thousand of items on the screen simultaneously.
The regions have an area proportional to the number of clinical trials they contain allowing the user to identify patterns (wich population is the most studied, what compound is the most sudied, etc...)