One of the first projects I tackled at Applied Minds in 2002 was a relationship viewer to view the relationships of people, places and things. I used size and color to illustrate the depth of the connections between objects.
For instance a connection that was 1 ply out would be large and dark while a connection 3 plys out would be smaller and lighter as if it were farther away.
The design was implemented as a Java application with an initial data set from IMDB. Searches were initiated by entering a text string in an input box.