Circumplex Model of Emotion
The circumplex model [of emotion] focuses on determining how traits and emotions are structurally similar, and its underlying assumption is that a relatively seamless circular ordering, or circumplex, is an economical description of the relations among traits and emotions.
Plutchik, R. E., & Conte, H. R. (1997). Circumplex Models of Personality and Emotions. American Psychological Association. doi: http://dx.doi.org/10.1037/10261-000.