It's Strava's Global Heatmap, and here's a writeup I did on how to use it as a layer in JOSM: https://nuxx.net/blog/2020/05/24/high-resolution-strava-global-hea

It's Strava's Global Heatmap, and here's a writeup I did on how to use it as a layer in JOSM: https://nuxx.net/blog/2020/05/24/high-resolution-strava-global-heatmap-in-josm/ https://nuxx.net/blog/2020/05/24/high-resolution-strava-glob... Note, you need a paid account to access the high-res data.