GIS-Based Landslide Disaster Risk Areas and Ground Movements Mapping to Support Disaster Mitigation Activities (Case Study: Tasikmalaya Regency)

Tasikmalaya Regency is an area that is prone to landslides and ground movements. The availability of comprehensive and accurate information in controlling land use for regional development in areas prone to landslides and ground movements is very important for casualty prevention and other losses such as physical, social and economic. This information must be disseminated to the public as an early warning system to support disaster mitigation efforts. Identification of the characteristics of landslide and ground movement prone areas requires the mapping of risk areas to mitigate disasters. This can be done using Geographic Information System (GIS). This mapping activity was carried out using the method of collecting digital data from five vulnerability controlling factors of landslides and ground movements, namely rainfall, rock type, soil type, land cover and slope. The analysis is continued by weighting the factors that influence landslides and ground motion and then overlaying the five controlling factor maps (with their respective weight values) to produce a landslides and ground movement vulnerability level map which is then inputted into WebGIS. This map can then be used by local governments and the public as an information medium to support disaster mitigation activities.


INTRODUCTION
Landslides and ground movements can cause significant repercussions such as damage and loss. The losses experienced can affect local communities. These losses can be in the form of loss of human life, damage to property and disruption of natural ecosystems (Alhasanah, 2006). Therefore, it is necessary to take action, especially in productive areas, economic routes, settlements and infrastructure (Zakaria, 2010).
The availability of comprehensive and accurate information in controlling land use for regional development in areas prone to landslides and ground movements is very important for casualty prevention and other losses such as physical, social and economic.
Such information should be disseminated to the public as an early warning system. In some areas with high population density and pre-existing early warning systems, such information is not distributed evenly, leading to the possibility for differing perceptions. This may cause panic and chaos and in effect, greater loss of both property and life (Noor, 2014).
Efforts that can be done to minimize the impact of landslides and ground movements are through the recognition of the characteristics of vulnerable areas. To identify the characteristics of disaster-prone areas, the mapping of disaster-prone areas is needed (Rahmad et al., 2018). Disaster risk mapping is an activity that presents the consequences of a disaster (Aditya, 2010). The development of Geographic Information System (GIS) can provide accurate geospatial data information and an accurate analysis system. This supports mitigation efforts to prevent risks that have the potential to become disasters or minimize losses from such disasters (Faizana et al., 2015).
Geographic Information System (GIS) is a system or set of objects and ideas that are interconnected (interrelationships) and displayed as geographic information which can be presented as software technology. This technology can then be used as a tool for entry, storage, manipulation, analysis, and display of field conditions with the help of data and spatial attributes. Comprehension of the "real world" will be better if the processes of data manipulation and presentation related to geographic locations are understood. (Munir, 2014).

PROBLEM
The output target of this community service activity is to produce an information system that is directly accessible for the public regarding the mapping of at-risk areas in the Tasikmalaya Regency. This information system is a tool to support disaster mitigation activities in Tasikmalaya Regency. With information that can be accessed directly, the public can be more selective of residential choices, be more aware of disaster risks and be better prepared for potential disasters.

Mapping of Landslide-prone Areas
The Making of landslide-prone area maps is based on secondary data such as rainfall maps, geological maps, slope maps, soil type maps, land cover maps and data on landslides and ground movement events that have occurred in Tasikmalaya Regency between 2013 -2020.
Data in the form of rainfall maps, soil type maps, geological maps and contour maps are then inputted into a GIS software. The data entry process is done through a set of computers using ArcGIS 10.1 software. This output data is then used as a reference for mapping analysis of landslide-prone areas in the Tasikmalaya Regency.
Analysis of the landslide susceptibility map is carried out after the thematic parameter maps, namely rainfall maps, soil type maps, geological maps and slope maps of the area are available in the form of digital maps. Each type of map is classified based on scores and given weight, the scores are then grouped together and analyzed. The mapping was done using ArcGIS 10.1 software. In the mapping process, each parameter has a classification      (2004) Classification of the results uses score analysis and is carried out by classifying 4 types of landslide susceptibility, namely: low, medium, high and very high based on final score numbers. The greater the score number, the higher the level of vulnerability, by establishing the following score intervals: (Highest score -Lowest score) : (Number of class classification)

Creation of a WebGIS that can be accessed by the public for free
After the landslide vulnerability map has been prepared, the next step is to post various geographical information that can be accessed by the public. The developed system must be able to provide functional and non-functional requirements.

Overview of the Tasikmalaya Regency Area
Tasikmalaya Regency is an agrarian area populated by a religious community,    Table 2, then inputted into ArcGIS which will eventually be overlaid with other mapping parameters.

Soil Type
Soil type maps are generated from SHP data which is downloadable for free from the government's official website. The naming of soil classification to the determining of the sub-group levels are conformed to the Soil Taxonomy (Soil Survey Staff, 1990). To ease the scoring process of the soil types map, the distribution of soil types in Tasikmalaya Regency was classified, in accordance to the National soil classification system, into 6 soil types namely, Alluvial, Brown Forrest, Andosol, Red-yellow Podsolik, Latosol and Regosol. The soil types map scoring is based on Table 5.

Land Slope
The land slope conditions in Tasikmalaya     Based on the map, the Tasikmalaya Regency area generally has moderate to high levels of landslide and ground movement vulnerability. This needs to be watched out for because Tasikmalaya Regency has a high rainfall intensity. Generally, landslides and ground movements occur in areas that have high rainfall intensity, high land slope and land covers in the form of vacant lands, rice fields or grasslands that cannot hold water.

WebGIS contains various information about landslides and ground movements
in Tasikmalaya Regency that can be accessed by the public. The front page of this WebGIS can be seen in Figure 8.

CONCLUSION
This community service activity aims to create a landslide vulnerability and ground movement map using an estimation model sourced from the Research Center for Research and Development in 2004 based on the scoring of five parameters, namely rainfall map, rock type map, land slope map, land cover map, and soil type map. Based on this weighting, Tasikmalaya Regency was divided into 4 criteria of landslide susceptibility, namely Low, Medium, High and Very High. After the landslide vulnerability map was compiled, the next activity was to create a WebGIS that can display various geographic information of landslides and ground movements that can be accessed by the public. In addition, the WebGIS also contained posters concerning mitigation for landslides and ground movements.

ACKNOWLEDGEMENT
The author would like to express the deepest gratitude to the Perjuangan University Research and Community Service Institute for facilitating the implementation of this community service activity.