Appropriate Grid Size for Terrain Based Landslide Risk Assessment in Lantau Island,Hong Kong

Aided by raster-based Geographical Information System (GIS) function, one method for terrain based landslide risk assessment for Lantau Island of Hong Kong was given in the paper. In this method, slope, aspect, vegetation covered, geology, elevation and distance to drainage line were considered as landslide related elements, and each element as given different weight in landslide risk assessment matrix. In raster based landslide risk assessment methodology, the grid size (pixel) selection for dataset concerned is a key task and must be solved. To find the most appropriate grid size for each elements, 5m, 10m, 20m, 40m and 80m five kinds of grid size were tested in this study. Following the state that landslide risk assessment result is the key to evaluate the appropriate grid size, landslide risk assessment parameters characteristic, risk assessment results were analyzed and compared thoroughly, 20m grid size was found the appropriate grid size for the pilot area according to most features described in the paper such as area frequency for each kind of grid size, landslide frequency under each grid size, area frequency for each class landslide susceptibility under different grid size. Generally, the appropriate grid size selection for certain cases are connected to area of pilot region, user requirement, gromorphology and topography characteristics of pilot region, and other case sensitive elements. Based on the results obtained in the pilot area, one experimental formula was given for grid size selection of landslide risk assessment.