• The line of vision from a member of the audience to the actionoccurring on stage. Visibility varies greatly from one theater toanother, and set designers must keep these individual factors in mind.Walls can be dispensed with and doors and windows reduced to simpleframes to solve sight-line problems. When a director blocks out themovements of actors (see blocking), he usually viewsthese from seats in every section of the house to ensure that allof the audience can see the main action.