Monday, April 13, 2020

Pinnacle Markers

Last week the New York Times mapped the rise of the death toll from coronavirus in the US over time. In See How the Coronavirus Death Toll Grew Across the U.S. the Times used an animated map to visualize the incredible spread of coronavirus in the United States in just over a single month.

The shocking rise in the number of deaths is dramatically visualized using triangular markers to represent the number of deaths from Covid-19. As you progress through the last month the triangular markers grow & grow on the map. In particular the marker representing the number of deaths in New York can't be ignored as it just shoots off the top of the screen.

It has become almost standard practice in mapping the spread of coronavirus to use proportional circles to represent the numbers of deaths. One potential problem with  proportional circles is that the largest circles can end up obscuring smaller circles at other locations. This can be seen in the New York Times' own Coronavisrus Latest Map and Case Count.

The thinner triangle markers on the latest NYT map work better in visualizing the huge numbers of coronavirus cases we are now seeing in the USA. Although they aren't perfect and the massive New York triangle does end up obscuring a number of locations to the north as it continues to grow in size.

If you want to use triangle markers in your own interactive mapped visualizations then you might want to check out the Pinnacle Marker plug-in for Leaflet.js. This plug-in allows you to easily add scaled pinnacle markers to a Leaflet map with options to scale both the height and width of the triangle markers based on your underlying data.

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