Yeah, things like location engines aren't for an outdoor citywide deployment, they're really more for trilaterating your position within a controlled area so yo

Yeah, things like location engines aren't for an outdoor citywide deployment, they're really more for trilaterating your position within a controlled area so you can localize someone's device to one corner of the office. It also helps if you have information on the floor plan so you can adjust the signal strength for attenuation from walls -- that's the kind of precision you're looking at. On a citywide level, though, you don't need that to get an idea of where people have been bringing their phones, just the detection by the access point in question is a major piece of information, readily placing you within a block or so of most APs. Of course, besides the wifi angle, the cell phone companies have something a lot like this too, and sometimes sell it or give it to law enforcement anyway.