Visibility analysis in urban spaces: a raster-based approach and case studies

In this paper a method for the estimation of the visual impact of buildings with symbolic relevance, such as skyscrapers that are out of scale with their surrounding urban space, is discussed and applied. It is based on the viewshed analysis as developed in rural landscape studies, but it also takes into account the peculiarity emerging from the urban studies. In order to go beyond the sole information of whether a cell is, or is not, visible, which is typical of viewshed analyses, in this work the various factors that cause the visual attenuation with the distance are discussed and quantitatively assessed by determining various limit-of-visibility distances that may also be time variable. These factors are the visual acuity, the contrast between the target and its surroundings, the atmospheric visibility, and the recognition process of the subject. An application of this methodology is carried out on various case study buildings in the city of Turin, Italy (an ancient building, an urban landmark, the Mole, and a skyscraper under construction). From the visibility maps, under various conditions, it can be seen that the new skyscraper will be a major landmark not only for the entire city, but also for the surrounding municipalities.