A sightline is a straight line from an audience member's eye to a point on the stage, and the question it answers is brutally simple: can that person, in that seat, see that thing. Every set design is a set of promises about what the audience will see, and sightlines are where those promises get tested against the geometry of an actual room.
The reason they deserve their own article is that sightlines fail quietly. A design can be beautiful on the model, correct at the workshop and completely wrong for forty seats on one side of the house, and nobody finds out until the first preview, by which time the fix costs a build day instead of a pencil line.
Try the free sightline checker: give it four measurements of your room and it draws this construction for you. No account needed.
The seats that decide the design
Start with the extreme seats to find likely problems, then check other positions where scenery, masking or the room changes the view. A clear view from the extremes does not prove that every seat between them is clear.
- The end of the front row, on both sides. This is the horizontal extreme: the seat furthest off the centre line and closest to the stage, with the most acute angle across the playing area. It is the seat that sees into the wings, sees behind flats set at an angle, and loses anything played hard against its own side of the stage.
- The front row centre. The vertical extreme from below. This seat looks up at the stage, so it loses anything low behind anything else, and it is the seat most likely to see the underside of a rostrum or the lighting rig above the masking.
- The back of the balcony, if there is one. The vertical extreme from above. This seat looks down, so it sees floor, sees over low scenery, and is the first to notice that a raked platform reads as a flat surface from up there.
These positions are a useful starting point. Add checks for each seating bank, balcony, local obstruction and important acting position in the actual venue.
Two drawings, because a sightline has two dimensions
Sightlines are checked on paper in two directions, and neither drawing can do the other one's job.
Horizontal sightlines are checked on the groundplan. Take the extreme seat, draw a line from it past the edge of the proscenium or the downstage end of the masking, and continue it upstage. Everything on the far side of that line is invisible to that seat, and everything on the near side of it, offstage, is visible to that seat. Those two facts are the whole of horizontal sightline checking: the first tells you where an actor can be lost, the second tells you where the crew, the ladders and the back of the scenery have to hide.
Vertical sightlines are checked on the section, which is the same room seen from the side. Take the eye height of the seat, draw a line to the point on stage that matters, and see what it passes through on the way. A seated eye is roughly 1.1 to 1.2 meters above the floor it sits on, so the front row of a flat house is looking up at a stage that is often about a meter above them, and the balcony is looking down over a masking border that was set for the stalls.
If a design has any height in it at all, and most do, checking only the plan is checking half of it.
What you are checking for, in both directions
There are two failures, and they are opposites.
Not seeing what they should. The actor at the upstage corner, the letter on the table, the face of somebody sitting on the low sofa behind the rostrum. Anything that carries a moment has to reach every seat you sold, and the further upstage and the further off centre a moment plays, the fewer seats hold it.
Seeing what they should not. The stage manager's desk, a crew member waiting to enter, the unpainted back of a flat, the wall of the building past the end of the masking, the fluorescent light in the wing. This is the failure that gets discovered by an audience rather than by a designer, because a designer standing centre stage never sees it.
The second failure is why masking is half of sightline work. Legs, borders, a false proscenium, a hard portal or simply another flat set further downstage exist to give the extreme seats something deliberate to look at instead of the truth. Designing masking is designing what the audience is not allowed to see, and it is easier to do while the plan is still a drawing.
The configuration changes the question, not the method
In a proscenium house the arch does most of the masking for you, and the sightline problem concentrates at the edges of the opening.
Push the audience around the stage and it changes shape. On a thrust, the seats at the ends of the side banks look straight across the stage at the far bank, so anything solid in the middle blocks somebody, and the design shifts to low furniture, floor treatment and things flown or set upstage. In the round, every direction is somebody's front, height is the only reliable tool, and the argument for a low set is not aesthetic but geometric.
The method does not change. Find the extreme seats, draw the lines, see what they cross.
When a sightline fails
Four moves, roughly in order of cost:
- Move it. Bring the piece downstage or toward the centre, where more seats hold it. Most sightline problems are solved by half a meter.
- Turn it. Angling a flat or a sofa a few degrees can open a view without moving anything, and often improves the picture anyway.
- Change the height. Raise what has to be seen, lower what is in the way. A rostrum solves upstage visibility for the same reason it creates problems for the front row, so check both extremes after every change.
- Re-block it. If the design has to stay, the moment can move. A director would much rather hear this in the design meeting than at the dress.
The one option that is not on the list is hoping. A seat that cannot see the moment will not learn to.
Checking without building a model
Traditionally the extremes get checked twice: drawn on the plan and the section, then looked at in the white card model by lowering an eye to the model's front row. Both are good, and the model is genuinely convincing in a way lines on a plan are not.
Setplot derives its 3D model from the groundplan as you draw. Choose a position along a seating bank to inspect the view, and use the plan’s sightline lens to highlight areas hidden by scenery or the stage opening. The banks initially use estimated dimensions based on the stage; enter your venue’s bank measurements to make the model closer to the room.
These are design checks using simplified geometry, a fixed eye height and sampled bank positions. They do not model seating rake, balcony geometry or the people sitting in front of a viewer. Check important views against measured plans, sections and the actual venue before relying on them.
The point of doing it digitally is not that it replaces the drawn check. It is that a check costing ten seconds gets done after every change, and a check costing an afternoon gets done once, usually too late.
The habit worth forming
Check the extremes at the sketch stage, before anything is decided. Check them again when the set is placed. Check them a third time after the last change, because the last change is the one nobody checks.
A design that works from the middle of the stalls is not finished. A design that works from the worst seat in the house is.