Open a map app and you get a dot so crisp and certain that doubting it feels rude. But accuracy is a moving target, and the interface is politely hiding just how much it moves.
In open sky, modern GPS can be accurate to roughly three to five metres. Step into a city and tall buildings bounce the signals around in a phenomenon called multipath, and your dot can drift across the street or down the block. Go indoors, into a basement, onto a train, and satellite reception collapses, leaving your phone to guess from wifi networks and cell towers with accuracy measured in tens or hundreds of metres.
This is why that faint blue circle around your position matters more than the dot itself. The circle is the phone's honest confession of uncertainty. A tight circle means high confidence. A circle that swallows three streets means the phone is essentially shrugging while trying to look composed.
Weather, solar activity, a case that blocks the antenna, an old phone, being deep in a valley, all of it nudges the numbers. The point is that phone location is a best estimate dressed as a fact. It is usually good enough to find a restaurant. It is often not good enough to prove where a specific human being stood at a specific minute.
That gap between "roughly here" and "exactly there" is precisely where a lot of jealous imagination goes to work, filling the fuzz with a story. Our GPS versus GSM piece explains why the fuzz exists.
The reassuring truth, and the one this whole site is built to deliver with a smile, is that location data is far blunter than the movies pretend. If you are ever tempted to build a case on a blue dot, remember that even the phone is not sure. Better to ask the person than to interrogate a circle.