Originally Posted by mibike

You can use RideWithGPS for this. Pair your RWGPS account to your Germin Connect account. When you finish a ride and it uploads to your Garmin account it will also be sent to your RideWithGPS account, While viewing the map if in planning or edit mode there is a Heatmaps drop down select Personal Heatmap. If not in planning or edit mode under the Settings drop down select Personal Heatmap. This will show all your rides with a purple line. It will also get darker and wider so you can see which roads you ride more then others,

There is also a Global Heatmap that shows where others ride. It can help with planing a ride in an area you don't know.