Not necessarily directly. It could work by saying "Here's a list of SSIDs I can see", to which the server responds "You're probably at [<lat, long, confidence>,

Not necessarily directly. It could work by saying "Here's a list of SSIDs I can see", to which the server responds "You're probably at [<lat, long, confidence>, <lat, long, confidence>, ...]". Under such a system, you'd have to know the SSID ahead of time, which probably means you're in close proximity to it already.