Using the HTML5 Geolocation API » SitePoint

Knowing the location of your users can help boost the quality of your website and the speed of your service.

In the past, users had to actively input their location and submit it to a site, either by typing it, using a long drop-down list, or clicking a map. Now, with the HTML5 Geolocation API, finding your users (with their permission) is easier than ever.

Read up the geloaction HTML5 API at Using the HTML5 Geolocation API » SitePoint.