## 3 Data Used  
A geographic information system (GIS) database including landslide inventory and affecting factors was created for the landslide spatial analysis. A landslide inventory map records the locations of landslides and other information, such as the date of occurrence and the types of ground/rock mass movements wherever available. Landslide inventory, in this study, was created from 248 historical landslide events which were identified and mapped in the study area by interpreting air photos, Landsat imageries, and Google Earth images. Field surveys were carried out under a national project in Vietnam for checking the ground truth of the occurrence of landslides (Figure 1). The largest landslide event involving 100,000 m\({}^{3}\) volume was recorded at the Che Cu Na commune (2011). The types of landslides, which occurred in the study area, included translational (35 events), mixed (36 events), toppling (45 events), rotational (124 events), and debris slides (8 events). Landslide affecting factors (parameters) such as slope, aspect, profile curvature, elevation, distance to rivers, river density, curvature, distance to roads, road density, plan curvature, distance to faults, fault density, land use, lithology, and rainfall were considered for the landslide analysis as they are known as important factors to landslide occurrences in any area [42, 43]. More specifically, slope affects landslide occurrences, as landslides often occur at certain critical slope angles depending on the nature of the ground mass and orientation of the sliding plane [44, 45]. This aspect is related with precipitation falling on the slope, solar radiation, soil conditions, and vegetation; thus, it is considered one of the condition factors in landslides [44, 45]. Profile curvature, plan curvature, and curvature represent the morphology of the surface which control the run-off and accumulation of surface water; thus, they have an effect on landslide occurrences [44]. Elevation is considered as one of the condition factors in landslides, as it is related to the weathering of soil and rocks on the slope [45]. At higher elevations, the weathering is generally much less. Distance to rivers and river density are landslide conditioning factors, as the ground mass near rivers is generally more saturated with water and a high-density drainage area drains out more surface water (run off) [44]. Distance to roads and road density affect landslide occurrences, as excavation for roads create more instability in the ground/rock mass, thus more landslides [44]. Distance to faults and fault density are considered as conditioning factors in landslides, as faults themselves cause landslides and ground/rock mass near faults are generally more fractured and vulnerable to sliding [44]. Land-use patterns greatly affect landslide occurrences. Landslides occur more in barren lands and in areas of agricultural activities [46]. Lithology is also considered a landslide conditioning factor, as the physical properties of soil and rock materials including their strength, porosity, permeability, and weathering affect sliding [45]. Rainfall is considered as one of the triggering factors in landslides, as it reduces soil cohesion and increases the pore pressure [47], and its influence on slope stability also depends on the duration and intensity of the rainfall. In this study, the factor maps were generated from a digital elevation model (DEM) with a 20 m spatial resolution constructed from contours extracted from topographic maps at a 1:50,000 scale, a geology map at a 1:50,000 scale collected from the Vietnam Institute of Geosciences and Mineral Resources, Google Earth images, and meteorological data on the area, which were classified into different classes, as shown in Figure 2, in the raster format of 20 m resolution.