Google Earth is a virtual globe program that was originally called Earth Viewer and was created by Keyhole, Inc. It maps the earth by the superimposition of images obtained from satellite imagery, aerial photography and GIS over a 3D globe. It is available under three different licenses: Google Earth, a free version with limited functionality; Google Earth Plus, which includes a few more features; and Google Earth Professional, intended for commercial use.
Formerly known as Earth Viewer, Google Earth was developed by Keyhole, Inc., a company acquired by Google in 2004. The product was renamed Google Earth in 2005 and is currently available for use on personal computers running Microsoft Windows 2000 or XP, Mac OS X 10.3.9 and above, Linux (released on June 12, 2006), and FreeBSD. In addition to releasing an updated Keyhole based client, Google also added the imagery from the Earth database to their web based mapping software.
The resolution is high enough in many large cities, such as Adelaide, London, Washington, D.C., and Seattle, that it is possible to clearly discern individual buildings, houses, the color of cars, and even the shadows of people and street signs.
The degree of resolution available is based somewhat on the points of interest, but most land (except for some islands) is covered in at least 15 meters of resolution. Las Vegas, Nevada and Cambridge, Massachusetts include examples of the highest resolution, at 15 cm (6 inches). Google Earth allows users to search for addresses (for some countries only), enter coordinates, or simply use the mouse to browse to a location.
Google Earth also has digital terrain model data collected by NASA's Shuttle Radar Topography Mission. This means one can view the Grand Canyon or Mount Everest in three dimensions, instead of 2D like other map programs/sites. Since 23 November 2006, the 3D views of many mountains, including Mount Everest, have been improved by the use of supplementary DEM data to fill the gaps in SRTM coverage. In addition, Google has provided a layer allowing one to see 3D buildings for many major cities in the US and Japan.