Creating Risk Maps with SuperGIS Custom Tool
Due to the rapid advancement of chemical research and engineering in modern times, people are using more and more new chemical compounds in our daily lives. In the manufacturing process of producing high-tech products like semiconductors or fire-retardant materials, it is inevitable to use to toxic substances or highly hazardous chemicals. For the government, to protect citizens from related incidents, it is critical to regulate and manage these factories and set up emergency response plans according to their sites.
Taiwan, as one of the highest populated countries in the world, a mild leak or spill may lead to numerous casualties. Therefore, the government plays an even more crucial role than the countries that have enough space to establish these factories in an isolated area.
Under Taiwan’s Environment Protection Administration, the Department of Environmental Sanitation and Toxic Substance (DESTS) is the authority to make emergency response plans for chemical accidents.
When the accident happens, the diffusion pattern of toxic spills would be affected by various factors, which result in spatial differences in the concentration of poisonous chemicals. Therefore, it is necessary to select customizable GIS software to create accurate risk maps and use them to make thorough emergency response plans.
For reaching the goal, the response team chooses a raster-based estimation method called “Inverse Distance Weighted” interpolation (IDW) to generate risk maps. Therefore, various environmental factors have to be integrated into a sample point layer. The detailed data processing steps are listed below.
Firstly, the local response team used a program- Areal Locations of Hazardous Atmospheres (abbr. ALOHA) to estimate the risk factor and the size of impacted area of a chemical accident. Because factories produce different materials, the impacted area may vary between them.
After acquiring these data, the next step is to integrate the risk factor and the affected area with the location of factories and show them on the map. The locations of plants are imported and converted to spatial data by the function “Add XY Data” in SuperGIS Desktop.
Fig.1 Using Add XY Data to Map the Factories
Fig.2 Creating Buffers According to ALOHA Results
For the next step, the analysts use a custom tool developed by Supergeo Project Team to generate evenly distributed sample points and integrate environmental factors as the weight of IDW estimation. In this case, the analysts add meteorological conditions like wind speed and direction and the buffer calculated by ALOHA into this VBA-based custom tool. After the calculation, it is the time to use these weights in IDW interpolation analysis to create risk maps.
By adding the factor of population density with Field Calculator, the analysts could conduct the analysis again and obtain more realistic risk maps.
Lastly, the extraction tool can cut the unnecessary parts of the risk maps with an administrative boundary layer and export the final result for the decision maker.
Fig.3 Producing Risk Maps with IDW Method
Results & Benefits
By using the custom tool of SuperGIS Desktop, the local response team of DESTS successfully created risk maps for emergency response plans. The risk maps show that the areas have many factories are not always the most dangerous. In fact, after considering the toxicity, population density, and wind speed and wind direction, even some distant villages are very probable to be threatened by chemical accidents.
The custom tool of SuperGIS Desktop provides extra flexibility and convenience to GIS analysts. With basic programming skills, users can quickly build a tool that can exactly meet their unique needs. In this case, the custom tool perfectly integrates meteorological conditions and population distribution into the IDW analysis, helping the response team make better deployment and preparedness according to more realistic and precise risk maps.