In a forum post a user asked if there is a way to create heatmap-style plots on a map. e.g.

It looks like MapBox supports a heatmap layer that would support this (See https://www.mapbox.com/mapbox-gl-js/example/heatmap-layer/), so it would be nice to add support for this layer type in the future.
+, would be a very useful feature
Seconded!
Thirded
Definitely useful.
done in https://github.com/plotly/plotly.js/pull/3993 - merged in master via https://github.com/plotly/plotly.js/pull/3987
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Thirded