Thanks for sharing the code on github.
I added a new feature to track SHIFT key-presses for symbols like # or @ in all three current keyboard layouts. I also took the liberty to clean up the formatting in index.html, if you don't like that part, you can just cherry-pick zaki/Keyboard-Heatmap-1@ecabeff.
The way it works is pretty general, so adding new modifier keys is just adding another pair of x,y coordinates in keyboard-layouts.js.
Adds shift key tracking for symbols
Looks fine, thank you for your contribution