180 degree rule

The 180 degree rule is as filming guideline that participants in a scene should have the same left-right relationship to each other, with filming only taking place within the 180 degree angle in which this is maintained in a conversation for example.

For example in King Vidor's The Big Parade (1925), the audience's viewpoint is constantly southward of the action- the American soldiers walk from left to right to the front-lines, and right to left when they return home, creating a continuous sense of direction.

This allows the audience to have a greater sense of location in the scene in terms on what may be off-screen in some shots, for example in shot reverse shots.