Visual Impact Assessment of Tehran Towers on the Observer's View

Landscape arrangement significantly influences the observer’s visual experience of the environment. Since measuring this qualitative experience is based more on personal judgments than on mathematical techniques, the representation of “quantifying methods” in this field demands a significant amount of caution and accuracy. This research is an attempt to quantify the visual impacts of seven-storey and higher buildings on observers’ views of Tehran’s District 3 from 1993 to 2006. For this purpose the visibility of the surrounding landscape to observers was computed for seventeen random points of the region, at 1.5m and 10m, before and after the construction of towers in that period, by the use of the Geographical Information System (GIS, Arcmap V.9.2) (in this research, seven-storey and taller buildings are considered as towers). For calculating visibility, the “Viewshed” tool in Arcmap was used, which reproduced accurate and quantitative data of changes in visual capability resulting from new obstacles in the view line. The result of this research indicates that the visual capability of citizens of Tehran decreased from 13% in 1993, after the construction of 12 towers, to 45% in 2006 after the construction of 255 towers. Also assuming this rate of construction continues in District 3, by 2013 the citizens will experience a 60 per cent decrease in the visibility of the surrounding landscapes, and an 80 per cent decrease by 2024. The objective of this research was to assess the visual impacts of structures on the landscape and to attempt to clarify the necessity and importance of applying VIA (Visual Impact Assessment) among other environmental assessments in new urban developments.