180 and 30 Degree Rule

In film-making, it is important to keep the film flowing, with no interruptions to disrupt the audiences viewing experience. We call this continuity editing. The purpose of continuity editing is to make sure that any signs of discontinuity made apparent during the editing phase are smoothed out, in order to make sure that the shots cohere with each other.
The two basic rules of continuity are the 180 degree rule and the 30 degree rule.

THE 180 DEGREE RULE

The 180 degree rule states that two (or more) characters in the same scene must stay in the same left/ right position to each other. For instance, if Character A were sitting on the left facing to Character B, who is sitting on the right facing to the right towards Character A, they must not at any time face in the opposite direction to the one they were originally facing. This would disorient the viewer and disrput the continuity of the scene.

The image above shows a red line connecting the figures. In order to keep to the 180 degree rule, the camera must not move over the line to the left hand of the characters facing right.

THE 30 DEGREE RULE

The two shots above show the breaking of the 30 degree rule. The camera must move at least 30 degrees in agle between two shots of the same subject. By doing this, we see a substansially different shot of the subject without it looking too close to the previous one. By obeying the 30 degree rule we avoid making it look like a jump cut, which can be distracting for the viewer.

However, we need to avoid moving the camera around too much, so as to avoid breaking the 180 degree rule.