I always figured they got the location of my wifi access point by driving by my house when they take all those pictures for Street View, but it turns out anyone walking by my house with a mobile device in their pocket might map my house. Anyone. Any phone. Any tablet.
It works like this: by default you anonymously share location data with your provider and it's really hard to turn off. By default your GPS is turned on. By default your WiFi is turned on. By default, you are a walking WiFi mapper because your phone tries to connect to my WiFi and then tells your phone developer about it -- Google, Apple, Microsoft... They all do it because, hey, it's free mapping for them, so why not?
I dug into this when I was staying at some remote house in a private development where there was no Google Street View, but they still showed my location within 100 feet. Google can't get into the compound with their cars, but they can still get in. Because I bring them in with my phone... And everyone has a phone, so even if I decide to castrate my phone by disabling a bunch of features, they'll just get it from someone else.
This means that private property isn't private property when it comes to your WiFi enabled devices. If Google can read my WiFi access point and map it using your GPS enabled phone, then they can map other devices that are broadcasting on WiFi like your SmartTV or AppleTV. They can take an inventory of your computer equipment...
This turns out to be one of those privacy things that no one cares about because no one really knows about it. There was a bill introduced in the US Senate in 2011 to limit government misuse of this information, but it doesn't really address the issue that we are quietly giving away not just our movements but that we're letting our phones probe the world around us and tell a big data center about it.
Not that it matters much anyhow as even the 3 year old bill still hasn't gotten any traction (see: http://en.wikipedia.org/wiki/Geolocation_Privacy_and_Surveillance_Act).
My phone knows where I am even if it doesn't tell me it knows where I am. When I had dinner at the fancy lodge last night, Google knew it. Apple probably knew too, because Markie has an iPhone.
Now, don't get me wrong, I don't think Google and Apple are going to do anything nefarious with this information, but it does bother me that I didn't know I was helping them map other people's networks.
It's the basis of too many sci-fi thrillers where the ubiquitous technology turns out to being doing something sneaky when you aren't looking that makes me worry -- there are so many of these devices doing so many covert things that we really won't know how big a problem it is until... [insert scary music] it's too late.