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Last edited 03 Sep 2020
A sight line is an unobstructed line of sight (or view) extending from a viewer to some object or landscape in the distance. The sight line makes it possible for the viewer to see some object in the distance. If a sight line to an object is impeded, the viewer will not be able to see the object in question.
Sight lines are important concepts in various fields, such as urban planning, particularly junction layouts, theatres and stadia. If a theatre seat has good sight lines, the occupier of that seat will likely have a good view of all the stage; if there is a column in front or to the side, the viewer may have restricted sight lines.
Sight lines can be divided into two components: vertical and horizontal. If an audience member has good vertical sight lines, they may be able to see the top and bottom of the screen or proscenium. Good horizontal sight lines give a full view of the left-right horizontal extent of the screen or stage. It may be possible in a theatre or cinema to have good horizontal sight lines but not good vertical sight lines ie, the full width of the screen is visible but some of the lower section is obstructed due to the balcony of the upper circle.
An important consideration in cinemas, theatres and stadia is the ‘C value’. This is the vertical distance between the eye of the spectator to where it intersects the sightline of the spectator immediately behind (and above).
This is a three-dimensional corridor of sight between an observer and a location, monument or other object in the distance. For example, a tall building in London may be refused planning permission – or its height may have to be restricted – because it compromises the viewing corridor to St Paul’s Cathedral of a person 10 miles away in Richmond Park.
View corridors are designed to protect the view of important monuments, buildings or landscapes. They are also a mechanism for ensuring that the character of villages, towns and cities is not compromised by the rapid rate of development that sometimes occurs in urban areas.
Once a corridor is established, it becomes known as a ‘protected view’ or ‘protected vista’. London has 13 of them protected by the London View Management Framework. One of the protected views is that from Alexandra Palace in North London to St Paul’s Cathedral in the City.
 Related articles on Designing Buildings Wiki
- Architecture of concert stage designs.
- Avoiding planning permission pitfalls.
- Conservation areas.
- Detailed planning application.
- Environmental impact assessment.
- Listed buildings.
- National Planning Practice Guidance.
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