Pretty cool - if you look at the Strava global heat map, you can clearly see all the ski areas right down to the trail outlines. You can also see which trails are the most popular by intensity of the map. You can also see some open secrets if you look carefully.
https://labs.strava.com/heatmap/#15.65/-71.55456/43.96112/hot/all
https://labs.strava.com/heatmap/#15.65/-71.55456/43.96112/hot/all