The 180-degree line is not a theory question. It is whether shot 12-B can cut with 12-C. Mark it on the master before you draw coverage.
Draw the line on the master
Sketch two subjects and a line between them. Write “cam stays south.” Every over, single and OTS is a camera on that side. Eyelines then have a wall to obey.
Matching pairs
If A looks camera-left, B looks camera-right. Note it in the footer (looks cam L). Do not rely on the drawing alone; thumbnails get tiny on a shot list.
If you must cross
Board the crossing: a move, a walk that turns, a new establish. A jump across the line with no in-between is the mistake. Continuity notes.
Generators
Independent frames do not share a floor plan. Treat pass one as beat density, then impose geography by hand. AI storyboard generators.
FAQ
Does animation care?
Sometimes, when you cut like live action. Stylised 2D often ignores it. Still time the reel. Animation use case.
Where do I practise?
Open the demo and reverse one over. If the look flips, you felt the rule.