Is Google Earth, Digital Earth? Defining a Vision

The recent wave of interest in the geographic referencing of information and the growing number of web-based geographic applications is highlighted by the success of Google Earth and other geobrowsers.  This category of software bears a more than passing resemblance to the vision of a Digital Earth, a project proposed in 1998 by then US Vice-President Al Gore, as an ambitious global undertaking to build a multi-faceted computing system for education and research. We first present a short history of the federally sponsored Digital Earth Initiative that followed the speech and related, in cases ongoing activities world-wide. We enumerate the functional, content, interface and system architecture elements of the Digital Earth vision, and contrast them with those of Google Earth. While Google Earth is clearly not yet Digital Earth, we offer for discussion a geographic approach to advancing from a vision and a promising interface to the definition of a particular, comprehensive and buildable digital earth system. In proposing a multi-resolution, three-dimensional representation of the planet, into which we can embed vast quantities of geo-referenced data, (Gore 1998) Mr. Gore was elaborating on ideas first broached in his 1992 book, Earth in the Balance (Gore 1992). The following passages from the speech exemplify its visionary tone: Imagine, for example, a young child going to a Digital Earth exhibit at a local museum. After donning a head-mounted display, she sees Earth as it appears from space. Using a data glove, she zooms in, using higher and higher levels of resolution, to see continents, then regions, countries, cities, and finally individual houses, trees, and other natural and manmade objects. Having found an area of the planet she is interested in exploring, she takes the equivalent of a "magic carpet ride" through a 3-D visualization of the terrain. Of course, terrain is only one of the many kinds of data with which she can interact. Using the systems' voice recognition capabilities, she is able to request information on land cover, distribution of plant and animal species, real-time weather, roads, political boundaries, and population.  A Digital Earth could provide a mechanism for users to navigate and search for geospatial informationand for producers to publish it. The Digital Earth would be composed of both the "user interface"a browsable, 3D version of the planet available at various levels of resolution, a rapidly growing universe of networked geospatial information, and the mechanisms for integrating and displaying information from multiple sources.  The results of a current Internet search on the term digital earth present an incoherent picture of its statusor perhaps, a clear picture of incoherence. One might have presumed that a phrase with so much cachet several years ago would describe the portfolio of a significant educational or research undertaking by now. But in fact, most of the links returned by that search are for pages and sites representing defunct efforts. We contend this is unsurprising and masks the fact that much progress towards realizing Digital Earth has taken place and that it remains, as Mr. Gore recently remarked, a superior organizing metaphor for digital information (Butler 2006).