Application of spatial viewshed analysis in classifying scenic forests along the Badaling Great Wall

The scenic forests along the Badaling Great Wall (BGW) is 2 227.8 hm², with a forested area of 1 314.2 hm². The configuration and management of the scenic forests along BGW are important elements of the scenery. In this study, spatial viewshed analysis on ERDAS virtual GIS platform was used to configure the scenic forests along BGW. First, the scenic forests along BGW and a "tourist" were put in a virtual three-dimension space. The "tourist" viewed the scenic forests from 35 observation spots of different coordinates. The view ranges of the "tourist" were divided into three levels - close range (0~500 m), moderate range (500~1 000 m) and long distance (1 000~2 000 m). Then the view range and inter-visibility of the "tourist" at the three view range levels at every observation spot were recorded. Based on the view results, the scenic forests was divided into vision blunt, perceptive and sensitive areas. The results of the viewshed analysis were overlaid with vegetation and BGW forest origin data to generate a zone map. Then the landscape type of every patch of the scenic forest in the map was determined in terms of view perception. The results showed that the vision blunt area, perceptive area and sensitive area of the scenic forests along BGW were respectively 824.44 hm², 880.4 hm² and 3 247.77 hm², respectively, in the farthest view rang (2 000 m). Through overlay analysis, scenic forests along BGW were divided into 119 landscape patches. For management convenience, the patches were classified into 10 forest groups. The groups included protection shrubbery in vision sensitive area, protection forest in vision sensitive area, protection shrubbery in view perceptive area, protection forest in view perception area, protection forest in vision blunt area, sightseeing forest in vision sensitive area, sightseeing forest in vision perception area, sightseeing forest in vision blunt area, recreation forest in vision sensitive area and recreation forest in vision perception area. The study provided the scientific basis for scientific management of scenic forests along BGW.