Users can click on a specific value to highlight where it appears in the heat-map.
Making it interactive
Heat-maps are good at giving an overview but frequently users want to isolate specific data that’s particularly meaningful. So added interactivity: mousing over one of the values in the key fades all others back, so that particular range pops. Clicking one of the elements in the key fixes the highlight state (clicking another element shifts the highlight; clicking the first element turns the highlight off.)