Location Services? Detecting your location

I'd like to get a stronger idea of ho开发者_Go百科w websites like http://www.msn.com/ can detect where you are. I know that you can do this by IP, but that can be extremely inaccurate depending on your ISP.

What is the most accurate method of doing this on the web?

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The ways you can do this, in descending order of accuracy:

1. Geolocation API (requires user to have compatible browser and give explicit permission)
2. Profiling data from advertising network.
3. IP Geolocation (Free versions tend to be very inaccurate, you can pay for slightly more accurate data)
4. User entered data.