Ingress: Google is broadcasting your address to everyone.
algorithm.dk
algorithm.dk
If it's a fixed distance (radius) then only the angle can be randomised. This means that graphing even just a few points from a consistent location will lead to a circle centred precisely on the user's address. Even if it's only partial, an arc can be extrapolated to a circle without any loss.
Considering most of the alert events are location specific events (playerX captured/attacked/deployed portalX, linked portalX and portalY), playing the location based game exposes your location to other players.
Some points to quibble... 1) Not all game events, just most of them ;) 2) It's a point in time location. In my experience, most game events occur on your _new_ travel pattern (based on game play) 3) Comm messages can be sent from the web interface (intel) and can appear to originate from wherever you are zoomed in on the map.
I really enjoy the game, even if I am the product. So far since March, I've logged approximately 200 miles walked solely from playing the game and have visited historical and cultural sites that I didn't even know existed.