It seems like no two definitions of Digital Earth are exactly alike. That's because Digital Earth is more of an evolving concept than a finished product.
In general, the idea is to have some sort of system that allows a user to explore a digital representation of Earth at any scale, and obtain a variety of information about any location. That information can include imagery, weather, news, historical events, demographics, restaurants, pollution—basically the sum of all available information ever recorded about a place.
The term "Digital Earth" is often associated with a speech given by Al Gore in 1998, though the concept can be traced back further in academia and science fiction (see Snow Crash).
Google Earth implements many of Digital Earth's core concepts, such as a seamless view of Earth's surface with graphical layers and links to local information. It has also been faithful to the vision of a collaborative Digital Earth, where many contributors from around the world can add layers and content. Still, there is much work to be done, like deploying more sensors, building more layers, linking to existing information, and managing all of the data and sensors we already have.
Then there is another aspect of Digital Earth taking shape—moving the experience off of the desktop and even off of mobile devices. This can mean integrating Digital Earth into the built environment, such as using smart lighting on a freeway exit lane to indicate a traffic jam on the upcoming frontage road. This distribution method gives people access to local information without the need to own and operate a piece of technology. Think of it as, rather than getting on the Internet to check if it's about to rain, just looking up at the sky. The information isn't as detailed, but it's certainly more accessible and intuitive.
