The Strava Heatmap is a project that the company's Engineering team initiated to produce a tile source build from hundreds of millions of user uploaded activities.
It is currently integrated within the RouteBuilder product on the desktop platform (web). In this blog post I'll describe how to integrate the map tiles which I've imported into Gaia GPS into your own tracks and planning.
On Gaia GPS these are called "Map Sources".
Click on any of the linked images above - they will direct you to one of the MapSources.