Originally Posted by John N

To clarify, Strava's Heat Map (and probably the other heat maps too) are the aggregation of all submitted rides (bicycle miles), regardless of the number of riders, i.e. one rider submits the same 5 mile route 10 times (50 bicycle miles) versus a group of 5 riders submitting the same 10-mile route (50 bicycle miles). What this means is you have to be a little aware that a highly "popular" route in a city may actually be just one or two riders who use it to bicycle commute to work 6 days a week. On their commute, they might take a very busy road that a club ride would avoid.