A sightline, or sight line, is a normally unobstructed line-of-sight between an intended observer (or spectator) and a stage

Stage (theatre)

In theatre or performance arts, the stage is a designated space for the performance productions. The stage serves as a space for actors or performers and a focal point for the members of the audience...

, arena

Arena

An arena is an enclosed area, often circular or oval-shaped, designed to showcase theater, musical performances, or sporting events. It is composed of a large open space surrounded on most or all sides by tiered seating for spectators. The key feature of an arena is that the event space is the...

, or monument

Monument

A monument is a type of structure either explicitly created to commemorate a person or important event or which has become important to a social group as a part of their remembrance of historic times or cultural heritage, or simply as an example of historic architecture...

, for example. Sightlines are a particularly important consideration in theatre

Theatre (disambiguation)

Theatre or theater refers to representational performing arts.Theater or theatre may also refer to:In types of venue:* Theater , a building with a stage and audience seating for performances...

 and stadium

Stadium

A modern stadium is a place or venue for outdoor sports, concerts, or other events and consists of a field or stage either partly or completely surrounded by a structure designed to allow spectators to stand or sit and view the event.)Pausanias noted that for about half a century the only event...

 design, road junction

Junction (road)

A road junction is a location where vehicular traffic going in different directions can proceed in a controlled manner designed to minimize accidents. In some cases, vehicles can change between different routes or directions of travel.-Origins:...

 layout and urban planning

Urban planning

Urban planning incorporates areas such as economics, design, ecology, sociology, geography, law, political science, and statistics to guide and ensure the orderly development of settlements and communities....

. In cities such as London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

, construction

Construction

In the fields of architecture and civil engineering, construction is a process that consists of the building or assembling of infrastructure. Far from being a single activity, large scale construction is a feat of human multitasking...

 within sightlines is restricted to protect the most interesting views of famous landmarks

Landmark

This is a list of landmarks around the world.Landmarks may be split into two categories - natural phenomena and man-made features, like buildings, bridges, statues, public squares and so forth...

.

Objects that have a direct line of sight with one another are said to be intervisible.

Sightlines in theatres

Sightline criteria in theaters can include: the "isacoustic curve" defined by John Scott Russell

John Scott Russell

John Scott Russell was a Scottish naval engineer who built the Great Eastern in collaboration with Isambard Kingdom Brunel, and made the discovery that gave birth to the modern study of solitons.-Personal life:John Scott Russell was born John Russell on 9 May 1808 in Parkhead, Glasgow, the son of...

 in 1838 and applied at the Auditorium Building in Chicago and the Emery Theatre

Emery Theatre

The Emery Theatre, or Emery Auditorium, is a historic, acoustically exceptional theater located in the Over-the-Rhine neighborhood of Cincinnati, Ohio...

in Cincinnati; alternate row sightlines where each patron sees between the heads of patrons in the row in front and over the heads of patrons in the second row in front; next row sightlines where each patron sees over the heads of patrons in the row immediately in front; and basic considerations like pointing the chairs more or less toward the performance, being able to see the conductor in the pit, being able to see other patrons, being able to see actors on elevated scenery, and not being obstructed by a wall, railing, column, ceiling overhang, loudspeaker cluster, or any other obstruction. The design of sightlines includes considerations of how much of the stage and scenery each patron can see. For example can each patron see the top of the scenery or not, and can each patron see the whole stage floor or not? Design of sightlines is divided into two related exercises, vertical sightlines and horizontal sightlines. Design of proper sightlines includes resolving both technical and aesthetic issues. At issue is the emotional response of the audience: whether a performer can hold the audience's attention or not; whether the patron feels they had a "good" seat and their ticket was fairly priced or not; whether the audience gets the emotional impact of the performance or not; and whether the patron wants to come back and see another performance in that theater or not. Building codes restrict the maximum and minimum rise per row, limit the minimum width per row, limit the maximum deviation in the size of steps from row to row to achieve the curvature of the rake, and limit other aspects of sightline design.

Books on theater planning that discuss the design of sighlines.

C-Value

Good sightlines allow spectators to see all areas of a venue stage. It is recommended that a spectator's eye height must be not be lower than 800 mm above the stage.
The angle from a spectator's eyes to the top of the forehead of the person in front of him is called a C-value. The C-value is a value that helps produce a rake.

• D = the horizontal distance from the eye to the point of focus
• N = the riser height
• R = the vertical height to the point of focus
• T = the seating row depth