"POPULARITY" Map Set.

If you have a TopoActive map set, this is supposed to represent Garmin's secret sauce. Personally, I have never seen any indication that it does anything at all. If I understand it correctly, it is supposed to show you (for example) popular biking routes or popular trails. Since I've never actually seen it work, I don't know how this is indicated. Would guess heat map, but that's only a guess.

AFAIK, this feature is strictly for TopoActive maps, which are derived from plain old OSM maps. The data is crowd-sourced from Garmin Connect, I think. Some of the stuff I've seen for watches seems to indicate that it only applies to selected activities and only to round trip routing. Since I do not round-trip route, that might explain why I never see it. Or not.

Thank you for the info. I didn't see it do much either except change cursor colour and different  shading etc.

Thanks for the explanation.