The Situationist International (SI) was an international organization of social revolutionaries made up of avant-garde artists, intellectuals, and political theorists, prominent in Europe from its formation in 1957 to its dissolution in 1972.
In a dérive one or more persons during a certain period drop their relations, their work and leisure activities, and all their other usual motives for movement and action, and let themselves be drawn by the attractions of the terrain and the encounters they find there.
Chance is a less important factor in this activity than one might think: from a dérive point of view cities have psychogeographical contours, with constant currents, fixed points and vortexes that strongly discourage entry into or exit from certain zones.
Psychogeography is an approach to geography that emphasizes playfulness and “drifting” around urban environments. Psychogeography was defined in 1955 by Guy Debord as “the study of the precise laws and specific effects of the geographical environment, consciously organized or not, on the emotions and behavior of individuals.”
Another definition might be a collection of playful strategies for exploring cities with the purpose of getting people off of their predictable paths which forces them to see new relationships and details of their environment.