As the article mentions this tech has been in widespread use for over two decades now. You have likely used it on your phone today without knowing it. GPS is accurate but also very fickle (takes time to get a lock, battery hog, doesn't work great when surrounded by buildings, doesn't work great when inside a building, doesn't work in bad weather). Wifi data is plentiful today in every urban setting, and you can get an exact location in under a second.