Movie Narrative Charts (by Randall Munroe)
http://xkcd.com/657/
This infographic shows the interaction between various characters in movies. Though mainly intended for geek humor, some valuable insights can be drawn from such approaches nonetheless. It is effective at visualizing which events involve more complex interaction between key characters, while at the same time making it possible to see the narrative trail each character followed before that (surprisingly, the visual encoding is also perceptually clear enough). This approach could prove valuable in studying historical material with focus on interaction between key figures.