How to know the original country of a website?

[hwinnum]

I want to know the original country of a website. I noticed that Alexa website can often detect the original country of websites. For example, Alexa can detect that the original country of stackoverflow.com website is US (check this http://www.alexa.com/search?q=http://stackoverflow.com/&r=site_screener&p=bigtop) and so on. How Alexa do this? and how i can do this? Thank You..