Urban canyon

A street canyon (also known as an urban canyon) is a place where the street is flanked by buildings on both sides creating a canyon-like environment. Classic examples of these human-built canyons are made when streets separate dense blocks of structures, especially skyscrapers. These include the Magnificent Mile in Chicago, the Canyon of Heroes in Manhattan and Hong Kong's Kowloon and Central districts.

Urban canyons affect various local conditions, including temperature, wind, air quality, and radio reception, including satellite navigation signals.

Ideally a street canyon is a relatively narrow street with tall, continuous buildings on both sides of the road. But now the term street canyon is used more broadly and the geometrical details of the street canyon are used to categorize them. The most important geometrical detail about a street canyon is the ratio of the canyon height (H) to canyon width (W), H/W, which is defined as the aspect ratio. The value of the aspect ratio can be used to classify street canyons as follows:

A sub-classification of each of the above can be done depending on the distance between two major intersections along the street, defined as the length (L) of the street canyon:

Another classification is based on the symmetry of the canyon:

Another specific type is –

The effect of a street canyon on local wind and air quality can greatly differ in different canyon geometries and this will be discussed in detail in sections below.

Other important factors taken into account in studies of urban canyons are the air volume, orientation of the canyon (north-south, east-west etc) and the sky view factor.The air volume of the street canyon is the air contained within the buildings on either side which act as walls, the street which is the bottom boundary, and an imaginary upper boundary at roof level called the 'lid' of the canyon.

The sky view factor (SVF) denotes the ratio between radiation received by a planar surface and that from the entire hemispheric radiating environment and is calculated as the fraction of sky visible from the ground up. SVF is a dimensionless value that ranges from 0 to 1. A SVF of 1 means that the sky is completely visible, for example, in a flat terrain. When a location has buildings and trees, it will cause the SVF to decrease proportionally.

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Wikipedia