This is awesome! I've tried it on a few areas that I know well, and it really did a good job.

I really love running in new places as a way to explore my area as well as when I travel. I find there is something profoundly good about connecting with my surroundings that way. I use Strava Route Planner with the heatmap extensively, and now I think I'll be consulting this a lot.

My only suggestion is to show an elevation profile. There is already a hill preference slider in the settings, but the elevation profile would really make it great to look at.