A couple things to note as well.
GPS is more of a 'line of sight' thing. Triangulation is done by number of satellites relaying its information to the GPS unit, most times, you will not get a GPS signal while 'inside' because there is no Line of Sight. You will see that with a TomTom (I have one) and it takes a few moments for it to triangulate off that.
If you ever watched NCIS, their resident Geek, Tim McGee, for instance, references times when they triangulate a phone bouncing off cell towers, same with CSI. So the better question would be where you might be in relation to towers. If you are only getting weak cell service, you might be on the edge of the provisioned Cell towers, more likely from only 1. Triangulation requires a minimum of 2 towers, 3+ would make it more accurate.