A knowledge-based approach for inter-laye weighting in order to optimal route location using Geospatial Information System (GIS) (Case study: Ilam-Homeil road)

Consideration of comprehensive and exact criteria in the route locating stage can play a decisive role in reducing of costs, increasing the safety and accessibility of roads as well as protecting the environment. In this regard, several parameters such as Digital Elevation Model, land cover, population distribution, touristic areas, sunshiny level of roads during cold seasons along with distribution of rivers and fault lines are considered in optimal route location of Ilam-Homeil road. In this research, an approach is proposed in order to assign inter layer costs. According to the proposed method, a specific cost function is defined for each layer regarding its own characteristics and influence on final decision. The most outstanding advantage of this approach is that cost variations is not linear for different data intervals of each layer and the characteristics of corresponding layer is considered indefining relevant cost function. Then pair-wise comparison and Analytical Hierarchy Process (AHP) are implemented for relative weighting of layers. Accordingly, the short path analysis is applied to supply the minimum cost considering three different variants. In the first variant the traditional method is used for inter-layer weighting and opinions of experts are considered for relative weighting of layers. In the second variant, the only criterion is the slope variation in the study area. The proposed knowledge-based weighting method is applied in the third variant. According to the results, the main parameter for route location of available road has been the topographical condition of study area and less attention has been paid to other factors such as distance from fault lines and rivers, access to population centers and touristy areas. The proposed routes resulting from each variants are shorter than constructed road.