Google Earth Mash Ups
Google Earth is an online collection of zoomable aerial and satellite photos carpeting a 3D model of the Earth. Early in January 2007, Google unveiled new collections of resources related to specific places on the planet. Features such as buildings and roads have been a part of Google Earth since inception however this new content is what some are deeming the first attempt to build what might be described as a geographically indexed world encyclopedia. One such contributor of this new content to Google Earth is the United Nations Environmental Program which has handed over 35 years of Landsat photos that can be overlaid on Google Earth, showing changes in crisis zones where human expansion and climate change are causing irreversible damage to the environment.
Google is dominant at the moment in the online mapping community with over 200 million downloads to date. The Keyhole Markup Language (KML) is the standard which makes it simple for external forces to contribute geo-based location information to Google Earth. Online bulletin board sites such as the Google Earth Community include place marks links to thousands of KML files which automatically open Google Earth and "fly" the user to the referenced locations in dramatic fashion.
Check out the following: 10+ Cool things a GIS user might do with Google Earth.