说简单一点，KML就是Google earth使用的文件格式，详细一些的介绍摘录于下，更详细的介绍见：http://www.keyhole.com/kml/kml_doc.html

KML, or Keyhole Markup Language, is an XML grammar and file format for modeling and storing geographic features such as points, lines, images and polygons for display in the Google Earth Client. KML gives you the ability to:

• Specify icons and labels to identify locations on the planet surface
• Create different camera positions to define unique views for each of your features
• Use image overlays attached to the ground or screen
• Define styles to specify feature appearance
• Write HTML descriptions of features including hyperlinks and embedded images
• Use folders for hierarchical grouping of features
• Timestamp features for dynamic playback and animations
• Dynamically fetch KML files from remote or local network locations
• Return information to the source server to trigger view-encoded fetches of KML files based on camera changes

A KML file is processed by the Google Earth viewer in a similar way that HTML files are processed by web browsers. Like HTML, KML has a tag-based structure with names and attributes used for specific display purposes. Thus, the Google Earth viewer acts as a browser of KML files.