A framework for assessing tall buildings' impact on the city skyline: Aesthetic, visibility, and meaning dimensions

The impact of tall buildings on cities can be evaluated on several aspects. One of these aspects is the impression of these tall buildings on the cityscape, whereby observers judge these buildings based on their three-dimensional status in the city. Some of the criteria that influence this judgment are the status of visibility, meaning, and aesthetics of tall buildings in the city. In this research, the three aforementioned criteria have been investigated using an analytical network process (ANP) method. This multi-criteria decision analysis (MCDA) method is used to weigh the criteria and sub criteria of the research (according to 22 experts and by using Super Decisions 2.8 software). After determining the weight of each criteria, three tall buildings in Frankfurt including Main Tower, OpernTurm, and the European Central Bank were selected to compare their impact on the skyline of the city based on the three variables and their weight. To calculate the visual impact of these three buildings, the idea of square degree score has been used, in which the ratio of the visible surface of these buildings to the visual field of observers in urban open spaces, and in an area of 2500 m radius with a centralized building structure has been investigated by ArcGIS Desktop 10.5 software. In order to determine the effect of the meaning and aesthetics of these three buildings on the city skyline, a pictorial questionnaire was prepared and distributed among 420 participants. The participant's preferences were taken into account to assess the impact of tall buildings on the city skyline. In the next step, the weight of the criteria, which was obtained in the ANP method, was considered for the results of the visual, meaning, and aesthetic criteria of the three tall buildings of Frankfurt. Based on the technique for order of preference by similarity to ideal solution (TOPSIS), the priority of these buildings was identified in terms of impact on the city skyline. With regard to the impact of tall buildings on the city skyline, these three criteria, according to their weights, ranked as follows: the meaning criteria (with a weight of 0.436) had the highest impact, followed by the aesthetic criteria (with a weight of 0.340), and visual (with a weight of 0.234), respectively. Thus, based on these results it was found that the European Central Bank had the most positive impact (with a score of 0.471) on the city skyline, then Main Tower (with a weight of 0.467), and OpernTurm (with a weight of 0.061) respectively.