[paulgb]

Using a WebWorker as a tile server for more compressed underlying data is a clever approach!

Are you doing anything special to compute the totals in real-time, or just summing over the entire selection each time the cursor moves?

[alprc]

just summing the selection area around the cursor

[anakaine]

Displaying so many points is something spatial people have struggled with for a long time. Would you consider writing a leaflet plugin that helps with your approach?