The 180° rule

The 180° rule is a filming guideline which states that in a scene with two subjects present, an imaginary line should be drawn to connect both of the subjects. The camera can then move freely within this 180° arc to maintain the left-right relationship between both characters. If the camera cuts the line, the rule is broken and by filming from the 180° arc on the opposite side it would appear to the audience that the subjects have swapped positions. It is important to maintain the 180° rule so the audience does not get confused, and to ensure continuity in the scene. Filmmakers may break the 180° rule for effect, for instance in a movie about a character who has lost their sense of direction, breaking the rule may be appropriate to reflect how the character is feeling. This image demonstrates the swapping effect if the 180° rule is broken: