Analyzing the visibility of high-rise buildings in the urban landscapes using GIS (Case study of Sanandaj city)

Today, the issue of visibility assessment and visual impact (dominance) of a building on its surrounding context is considered as one of the most important issues of urban landscape. Accordingly, this paper analyzes the visibility of two high-rise buildings in the center and west of Sanandaj using raw input data and processing them by GIS and ArcGis 10. For the visibility analysis in urban landscape, the mutual visibility between high-rise building and its surrounding area is calculated. This is done traditionally by taking photos from urban areas. However, in this method, the whole region is studied by considering all points and places. The available vegetation such as trees with an approximate transparency ratio is considered to obtain more accurate results. Also, for better evaluation of differences between the amount and trend of visibility, the areas around both buildings (region number 1 is relatively flat and has a river-valley with low depth and mild slope; region number 2 involves dune hills) were classified into the close, intermediate and far fields. The visibility of these two high-rise buildings in their surrounding areas is in the form of output GIS images which is calculated separately for both buildings and all their floors. It means that for building number 1, which has 17 floors, 17 output maps of visibility to surrounding areas are obtained by the software. Also, for building number 2 with 14 floors, 14 output visibility maps are obtained. The findings show that visibility trend of different floors of these two buildings is not a constant and linear trend, it has variations in some points. Among these points, visibility and its effect, relative to surrounding areas, is more important than other floors in the triple fields. The points where visibility curve has track change, steep change and sudden increase show the greater importance of their visibility and their relative dominance than other floors. These floors can visually have more effect on their surrounding environment. Therefore, the design style of these particular floors (milestones in the visibility curve) in high-rise buildings can be important. The changes in floors visibility trend and their values were different for the two buildings. By evaluating the related diagrams, the reasons for this difference were found in three cases: first, the difference in average height of buildings around of two buildings; second, the difference between the tilt around the two buildings; and third, the dune hill in region number 2. Finally, we can say that visibility analysis is considered to be a tool for modeling the visibility in planning high-rise buildings. Before constructing such buildings, visibility analysis can be an effective method to estimate that a floor or an apartment will or will not have a good view after completion. Therefore, this tool can be used to investigate the positive or negative value of a region. Also, the extent to which a building is or is not visible can be very important in decisions about determining the height of a building relative to its surrounding texture (especially in cities with historically valuable texture and touristic landscape).