I found a similar question here but I still don't get it.

You see, I live in a small town and every time I check my IP location via online services or speed test websites, my location appears to be my ISP server location (which in my case is 250 miles away). But when I tried Google latitude, it pinpointed my exact location within less than 100 meters!

I use Windows Vista, Google Chrome, and when I got the message that "Google is trying to locate you", I agreed just to check what the result will be. It was scary, very scary!

What I've come up after reading the above link is that Google have a kind of extensive WiFi database locations. That could be understandable with the case of public and open WiFis that are used with a lot of people. Some of them might be using applications that could gather location data and somehow this information ends up in giant Google databases. From those, Google could pinpoint a WiFi location based on its MAC address along with these bits of info that have been gathered via various sources.

The issue here is that my WiFi is private, I don't even broadcast my WiFi name. So how on earth did Google find my exact PC location?

Please break down the answer in layman's terms as possible.