When I look at my heart rate plot, I often wonder why it goes up or down, and I would like to see the terrain at this location. Thus, it would be nice if the map view could overlay heart rate, cadence, speed etc over the course/map.
The "Player" feature of GC does what you are looking for here. While it doesn't specifically overlay the data on the map, it's all there so you can visualize your HR, cadence, power etc, and relate that to the terrain you were riding over.
