Basically this is the tactic to to denote a physical address map of a particular location in the website like city map or Google map. more specifically; KML is a file format (In human readable format) used to display geographic data in an earth browser, such as Google Earth, Google Maps, and Google Maps for mobile. KML stands for the Keyhole Markup Language. Since march of 2007 Google is indexing these files which can be included in your existing sitemap, or better, newly proposed geositemap. From the information that you provide in the KML map, Google will scrape after checking it's authenticity and will add your regular site map.
It's helpful for Google Map. Just paste "Geo tag generator" in Google and you'll get a website having domain extension name in .de. You can create your own by giving proper latitude, longitude and location.