(Still looking for a good name for this project...; X-Ray will have to do for now. I'm open to suggestions though.)
Take 2 of my software visualisation experment. (See here for take 1.) This time I managed to get some static info into the picture as well: the module in which the called method resides. I therefore decided to switch the visualisation to a treemap. Each rectangle represents one module, and is assigned one colour/hue. Sizes are relative to the number of methods which were used in that module.
The colour's saturation is a reflection of the number of times that method was called. So the less washed out a colour looks the more that method has been used.
I also experimented with plotting method exits but threw it out in the end for two reasons. One is that I couldn't get reliable data on all exits (about 10% went missing). The second is that it didn't make any notable difference to the visualisation anyway.