In theatre, blocking is the precise movement and staging of actors on a stage in order to facilitate the performance of a play, ballet, film or opera. the term derives from the practice of 19th-century theatre directors such as sir w. s. gilbert who worked out the staging of a scene on a miniature stage using blocks to represent each of the actors (gilbert's practice is depicted in mike leigh's 1999 film topsy-turvy). in contemporary theatre, the director usually determines blocking during rehearsal, telling actors where they should move for the proper dramatic effect, ensure sight lines for the audience and work with the lighting design of the scene. each scene in a play is usually "blocked" as a unit, after which the director will move on to the next scene. the positioning of actors on stage in one scene will usually affect the possibilities for subsequent positioning unless the stage is cleared between scenes. once all the blocking is completed a play is said to be "fully blocked" and then the process of "polishing" or refinement begins. during the blocking rehearsal usually the assistant director or the stage manager (or both) take notes about where actors are positioned and their movement patterns on stage. it is especially important for the stage manager to note the actors' positions, as a director is not usually present for each performance of a play and it becomes the stage manager's job to ensure that actors follow the assigned blocking from night to night. by extension, the term is sometimes used in the context of cinema to speak of the arrangement of actors in the frame. in this context, there is also a need to consider the movement of the camera as part of the blocking process (see cinematography).