Google recently released a beta version of its 3D mapping application that builds upon the Keyhole 2 LT application it acquired in 2004. Google Earth features satellite imagery of the entire planet, and like Google Maps, it integrates Google search results right onto the globe. It allows you to zoom from space right down to your city, take a virtual tour of the globe, or share what you've found by utilizing the XML data exchange system, KML.
Upside: One of the most useful features is layers, which show users restaurants, banks, bars, gas stations, hospitals, and more in the area, all with a single click. You can add or remove layers to suit your search. Google Earth will even display crime statistics, congressional districts, or postal code boundaries for a given zone. The tour feature allows you to bookmark and append your own descriptions to numerous places all over the globe, then fly between them with the earth spinning below--a very cool and quite addictive effect. Google Earth also features 3D terrain mapping, which is stunning at places such as the Hoover Dam or the Grand Canyon, allowing users to see the contours of the land (you'll have to install Google Earth in order to follow these destination links). Google has added 3D buildings in major U.S. cities, which offers a far richer 3D experience than the terrain alone. And unlike Keyhole 2 LT, Google Earth is free.
Downside: Unfortunately, Google Earth's high detail seems to be mainly centered on the United States; satellite imagery outside of the country is irregular. One example is in Melbourne, Australia, where half of downtown is crisp, and the other half is a blur. The free version lacks drawing tools and GPS data import; the Plus version adds these for $20. Also, Google Earth is only for Windows 2000 and XP.
Outlook: Google Earth is extremely flexible, even allowing users to create their own layers. As we saw with Google Maps, users were able to hack in features such as crime statistics and housing prices, and with Google Earth's more powerful engine, it's expected that additional creative features will be unleashed. Already, users have figured out how to create their own buildings, show real-time bus tracking, or even display the closest Flickr photos to their location.