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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 have an impact on various local conditions, including temperature, wind, air quality, and radio reception, including GPS signals. == Geometry and classification == 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. * Regular canyon - aspect ratio ~= 1 and no major openings on the canyon walls * Avenue canyon - aspect ratio < 0.5 * Deep canyon - aspect ratio ~=2 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. * Short canyon - L/H ~= 3 * Medium canyon - L/H ~= 5 * Long canyon - L/H ~= 7 Another classification is done based on the symmetry of the canyon. * Symmetric (or even) canyon - The building that make the canyon approximately have the same height * Asymmetric canyon - The building that make the canyon have significant height differences Another specific type is, *Step-up canyon - A street canyon with the height of the upwind building is less than the height of the downwind building 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 (being north-south,east-west etc.) and sky view factor.The air volume of the street canyon is the air contained within the buildings on either sides which acts as the walls, the street which is the bottom boundary and an imaginary upper boundary at roof level, which is called the 'lid' of the canyon. 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 when viewed from the ground up.SVF is a dimensionless value that ranges from 0 to 1. A SVF of 1 denotes that the sky is completely visible; for example, in a flat terrain. When a locations has buildings and trees, it will cause the SVF to decrease proportionally 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Street canyon」の詳細全文を読む スポンサード リンク
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