Google Earth

Google Earth is a Web-based mapping software (also characterized as a virtual globe program) that portrays a visually accurate representation of the entire earth surface using satellite images, aerial photographs, and GIS data. It is available on the Web in a free-of-charge version. Chargeable versions with enhanced capabilities are also available for professionals.

Google Earth was initially developed by Keyhole, Inc., under the name “Earth Viewer.” In 2004, Google acquired Keyhole and renamed the product “Google Earth” in 2005. Since then, a free-of-charge version has been available on personal computers running MS Windows 2000 or XP, Mac OS X 10.3.9 or later, and Linux Kernel 2.4 or later. In June 2006, Google Earth Release 4 was launched.

Google Earth provides images and photographs that cover the whole globe. They are taken sometime during the last 3 years and are updated on a rolling basis. The resolution varies from place to place. In general, it allows the user to see major geographic features and man-made development, such as towns and major roads. For most of the major cities in the United States, Canada, Western Europe, and the United Kingdom, the resolution is high enough (15 cm to 1 m) and reveals details for individual buildings and even cars and humans. In addition, for several U.S. cities, 3D buildings are represented. Google Earth also incorporates digital terrain model (DTM) data, which makes the 3D view of the earth's surface possible. The coordinate system used is the standard WGS84 datum. All images and photographs are georeferenced to this system. All terrain data and GIS data are also stored and represented in this datum.

Data provided by Google Earth are retrieved mainly from Google Maps and several satellite and aerial data sets (including private Keyhole images). DTM data provided by Google Earth are collected mainly by NASA's Shuttle Radar Topography Mission.

Google Maps is a Web map server (such as Mapquest or Yahoo!Maps) maintained by Google that provides high-resolution satellite imagery and aerial photography, international street-level data sets, and [Page 217]many map-based services. Through the Google Maps Application Programming Interface (API), the full Google Maps can be readily embedded on an external Web site for free. This API, along with others and the Web 2.0 technologies, led to an expansion of the socalled mapping mashups.

A mashup is a Web site or Web application that uses content from more than one source to create a completely new Web service. A map mashup combines map content from more than one source. As a result, digital maps are quickly becoming a centralized tool for countless uses, ranging from local shopping to traffic reports and community organizing, all in real time and right down to specific addresses.

The basic functionality of Google Earth may be summarized as follows. The user may browse to a location (a) by searching on addresses (this is available in the United States, Canada, and Western Europe only), (b) by entering the WGS84 coordinates, or (c) by using the mouse. Then, the user can zoom in or out and move or rotate around this location. The user may then turn on various layers of mapping information (GIS data), such as roads, borders, recreational areas, and lodging, or ask for driving directions and measure distances. Users may also add (using user-friendly interface) their own points of interest (placemarks) and other vector and raster data, including 3D objects and models (designed in a companion free software, Google SketchUp), either manually or automatically (by loading them from digital files or connecting to a GPS receiver). Finally, users may attach to their own customized hypertext documents written in html. At any time, they may save, print, e-mail, or make available to others what is on the screen.

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