I put together a short demo of loading and displaying 2 million waypoints (GPS locations) on an interactive map, to visualize all the places I have been riding my bike. All data processing and rendering is implemented in Racket:
The visualization scales up to at least 4.36 million points (which is the most I have to test with, if I include running, sailing and other activities), but it should be able to handle much larger number of waypoints.
Enjoy,
Alex.