Why We Love It

This map takes on a massive, complicated dataset— three decades of tornadoes in the US. We see different patterns each year for the number of tornadoes, where they strike, and the direction they travel. We love this map because it tells many compelling stories. We see, for example, that overall fatalities have declined through the years, but then we look at 2011 and see that we still have a lot to learn.

Why It Works

This map is exceptionally interactive and rewards you with every click. You really see the power and patterns of these storms as you zoom in to explore a region, click on symbols for details about a particular tornado, and select from the table to see incidents by year. You can also get a different perspective when you view by city, by state, or the entire US.

Important Steps

To recreate interactive symbols, examine your data and determine the number of categories (classes) to represent.

Create a PNG icon for each category, or use the samples provided in the additional resources at the bottom of the page.

Give your classes a single-color graduated scheme when they are not activated. Assign icons to each class to represent tornado strength (or similar method of increasing icon size to show value by category).

Create and assign an accompanying red highlighted icon that will become the activated symbol (one that has been clicked on).

Icons are associated with points in the JavaScript logic. For the click marker event, create code to present the red highlighted marker.



The data is simply one giant table of tornado events. It comes from NOAA’s SVRGIS. The app processes the raw data and presents a summarized view.


The tornadoes app is a custom story map, built with the ArcGIS API for JavaScript. We used Microsoft Access and SQL to get a quick summary of the data (useful for defining the class breaks).


It takes one day to create interactive symbols.

Dashboard Template


The dashboard template gives you a lot of complex information in one glance. Customizable graphs and tables are an alternative to using clickable pop-ups to present supplemental information.

Thoughtful Presentation


Take note of the map author's thoughtful presentation of data at all zoom levels, each with multiple interactive options to see a variety of patterns at different scales and time frames.

Data with Time or Date


Data with a time or date component can be a challenge to present in any map. However, the use of an interactive graph allows the audience to jump from year to year. The bars for each year also update based on the scale and location you choose.

More Information

Map Author

Allen Carrol

Allen Carroll


I grew up in the Midwest, loving maps and having occasional bad dreams about twisters. Current passions: story maps, birds, family.

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