In general, diagramming relations between characters by arrows or other lines between them -- a technique from fiction writing. In RPGs, it is suggested in "The Sorcerer's Soul" supplement for Sorcerer as a technique to help with scenario preparation. That recommends creating a map with only bonds of family relationship and sexual contact. See also Storymap

(Edwards has since clarified that relationships in question are simply a primary starting point, and that one may well add more relationships of additional types as neccessary.)

Early examples of relationship maps in RPGs can be found in White Wolf's Vampire line as early as First Edition city supplements in the early nineties. In those supplements, powerful elder vampires were laid out in diagrams with lines connecting them containing information about their relationships.

References:

• Relationship maps
• relationship maps and all that jazz
• Relationship Map development example