HTML5 is a language for structuring and presenting content for the World Wide Web, and is a core technology of the Internet. It is the fifth revision of the HTML (Hyper Text Markup Language) standard (created in 1990 and standardized as HTML4 as of 1997) and as of January 2012 is still under development. [Wikipedia]
HTML5 has dozens of cool new features that make creating highly interactive web applications easier than before. One of those cool features is Geolocation, which allows web users to share their location with a website.
I was recently working on a project for which I did some research on Geolocation and I came up with this page, which shows you your location on a Map. The page uses the Google Maps API to display the maps and uses your browser to determine your location.
You can look into the source code to see how to implement it to your own projects. It has been tested with the latest version of Opera, IE, Chrome and Firefox as of January 2012. One of the greatest resources to learn about HTML5 and its features is HTML5ROCKS.COM by Google.