This summer, the Esri Disaster Response Program has responded to several disasters, including floods, tornadoes, and wildfires to provide technical support, software, data and information maps. While we always provide public information maps, one of the most common requests we now receive is for help in understanding the potential impact of an event.
Using GIS for analysis, we create impact maps. These maps are designed to answer specific questions about a disaster, including what effect it may have on the population, local economy, and infrastructure. To create your own impact map, there are a few steps to follow.
First, you need to have an impact question. For example, “who lives in the flooded area?” or “how many houses are within the fire perimeter?” Next, you need a way to answer these questions, and finally a way to share the answers with a focused map. To answer the impact question, we use ArcGIS Online Geoenrichment. In this blog, we are using an example from the recent Silver Fire in Southern California, which grew to more than 20,000 acres and forced the evacuation of rural mountain communities. The public safety agencies wanted to know “how many people live in the area?” and “what type of housing do they live in?” Let’s step through the process we used to build the Silver Fire impact map.
Define an Impact Area
To start, we needed to define the area that was impacted. For this we used the US Wildfire Activity web map and applied a filter to the “Wildfire activity (USGS)” layer to find the impact area we were looking for – in this case the fire perimeter. Other options are to filter against place names from layers like incorporated towns, add files from your computer, or even use map notes to define your impact area.
Enrich the Impact Area
Now that we defined our impact area, we used the Enrich layer capability in ArcGIS Online to find out more information about the perimeter. One category that is useful for understanding the impact to citizens is “Key US Facts,” however there are several datasets you may be interested in for a wildfire, such as “Land Cover” and “Public Lands.” Once you have selected your data categories, the Enrich layer employs a sophisticated geographic retrieval methodology called Data Apportionment for aggregating data categories to your impact area (e.g. Key US Facts). Another source of demographic information available is Tapestry Segmentation Data, read this white paper to learn more about how this can be applied: “Identifying Special Needs Populations in Hazards Zones: How to Use Tapestry Segmentation for Disaster Evacuation Planning“.
Explain the Impact
The analysis will provide data – but it is up to you to present the information in a way that helps others understand the impact to the area. One way to do this is to configure you map to better tell the story. Start by customizing your popups as you see here. In this case, we used Pop-up Media to convey information using charts.
The final step is sharing your map to show the analysis of what could be impacted by the event. With ArcGIS Online you can share your web map as a link, send it out on social media, or publish it as a focused web mapping application hosted from ArcGIS Online. This is something you can practice now before disaster strikes your community.
We recognize the importance of these maps and the power of enriched data to help understand impact during times of disaster. Therefore, we are working on some new web mapping applications to answer impact questions more quickly and directly. We intend to use case studies like the Silver Fire, and your feedback, to turn these web mapping applications into ArcGIS Online hosted templates. An example of this process is the Esri Public Information Map, an application used by the Esri Disaster Response Program to provide situational awareness. While this application started as a prototype, it has since become the ArcGIS Online Social Media Template. Check out these impact map applications and other prototypes on the Esri Disaster Response Program website and give us your feedback.
Contributed by Paul Doherty, Public Safety Technology Specialist and Derrick Burke, Technology Team Lead