Although not officially part of the HTML5 specification, Geolocation has become one of a number of new technologies that have recently come to light with advent of HTML5. Remy Sharp and Bruce Lawson also felt it important enough to write a whole chapter about in their brilliant book, Introducing HTML5.
The Geolocation API is used to find the location of your users. You’ve probably noticed a similar technology on many apps used on smartphones — checking into places through Facebook or Foursquare, for example. The same can be done with most modern web browsers. When used in conjunction with the Google Maps API, you can get some pretty cool results and add some great features to your website or web apps.