John N Ah. Cool.
That is news to me that the data is "rolling" (IE - stuff 5-10 years ago isn't in the data set any more as its been phased out). I never heard the back story, either, that the data was a governmental/municipality supply of pedestrian data. That almost sounds like Google-type data collection, but if they are only gathering data off those users that upload data to Strava it would be a significantly reduced amount of data than, say, the "live traffic" feed from everyone's phones that have google services traveling on all the roads at any one time. If they (Strava - or what ever service actually collects the data) had the ability to ping everyone's phones that would surely be a lot more numbers, but I don't know how they would differentiate between activities (vehicular travel, biking, hiking, jogging, cross country skiing, kayaing, etc).
In any event, however it is done, the resultant "heat map" is, as discussed earlier, a very useful tool to tuck in ones' back pocket for routing purposes.