I've noticed that above a certain threshold distance, Strava tends to show me a map for a given activity in my feed, but below that threshold, I just see a bare summary of the activity: distance, maybe feet climbed, maybe time in motion (cycling) or pace information (running). The threshold seems to be about 5 miles, though sometimes I'll instantly see a track for something shorter. And I'll always see tracks for my own activities.
Behavior seems to be consistent between web and mobile. Anybody know what's going on here? It seems weird; I've been trained to think no map == this is an activity that someone entered manually, and there is no GPS data.