Point Based Assessment: Selecting the Best Way to Represent Landslide Polygon as Point Frequency in Landslide Investigation
Doctor, School of Environment and Natural Resources Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia.
Professor Emeritus, School of Geography, Environment and Earth Sciences, Victoria University of Wellington, New Zealand
Mairead de Roiste
Doctor, School of Geography, Environment and Earth Sciences, Victoria University of Wellington, New Zealand
Abdul Ghani Rafek
Professor, School of Environment and Natural Resources Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia.
This study evaluates two common methods to represent landslide polygons as frequencies for use within GIS analysis. These methods are used to extract information from factor maps, such as a single value for slope angle for the landslide polygon, which is then used in hazard assessment. Understanding the errors associated with generating points to represent landslide polygons should be clearly understood to evaluate the effectiveness of these points. In this paper, the effectiveness of two representation techniques in gathering slope angle information is examined. The first technique evaluated is based on the centroid (a point feature) of each landslide polygon. The value of the landslide factor class beneath the centroid point, e.g. the slope value at that point, selects the landslide factor class. The second method is an area based technique which depends on the area covered by different landslide factor classes, e.g. the most common slope for the polygon. Here, the landslide factor class that occupies most of the landslide polygon is selected as the attribute for each landslide polygon. As demonstrated in this paper, the results favour the area based technique. While this paper explores this technique for slope information, the finding is applicable to other landslide causal factors, such as elevation and rock type.
Keywords: Centroid point, area based technique, landslide, GIS.
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