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Open geocoding standards allow anyone to contribute to the Google Earth mirror world. Just as Web browsers depend on HTML to figure out how and where to display text and images on a Web page, Google Earth depends on a standard called KML, the keyhole markup language, to tell it where geographic data should be placed on the underlying latitude-longitude grid. If you know how to assemble a KML file, you can make your own geographical data appear as a new “layer” on your computer’s copy of Google Earth; and if you publish that KML file on the Web, other people can download the layer and display it on their own computers.

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This layering capability transforms Google Earth from a mere digital globe into something more like a 3-D Wikipedia of the planet. The results can be unexpectedly arresting. In one recent example, the U.S. Holocaust Memorial Museum worked with Google to create a layer highlighting the locations of 1,600 villages ravaged by the Sudanese government’s ongoing campaign to wipe out non-Arab tribes in the Darfur region. By zooming in on these locations, a user can see the remnants of the actual settlements destroyed by the Janjaweed, the government’s proxy militia. The closest views reveal that house after house has been reduced to a crumbling wreck–roofs burned away, contents apparently looted. Pop-up boxes contain testimony from survivors, statistics on the displaced populations, and dramatic, often grisly photographs taken in the field or at refugee camps [Google Earth link].

This evidence of genocide is attached to the same digital earth where most U.S. residents can quickly zoom and pan to North America and look down upon their own houses or their children’s schools. With the barrier of distance dissolved, it’s hard not to feel a greater sense of connectedness to tragedies abroad. Which is exactly what the Holocaust museum intends: “We hope this important initiative with Google will make it that much harder for the world to ignore those who need us the most,” museum director Sara Bloomfield said. (The Sudanese themselves cannot download Google Earth, owing to U.S. restrictions on software exports.)

Just as anyone can create a new layer for Google Earth, anyone with basic 3-D modeling skills can add buildings, bridges, and other objects to it. Google Earth uses the open Collada 3-D modeling format, which was originally created by Sony as a way to speed the development of video-game worlds for the Playstation Portable and the Playstation 3. Using a Google program called SketchUp, amateur architects have built thousands of Collada models and uploaded them to the Google 3D Warehouse, a free library of signature buildings and other 3-D models. Larger organizations around the world now have terabytes of Collada-formatted virtual objects in storage and can easily transform them into data layers for Google Earth. That’s what the city government of Berlin did in March, when it published a KML layer containing a meticulous 3-D model of the city, prepared as part of a new digital infrastructure for city management and economic development [Google Earth link]. The model is so finely detailed that a deft user of the Google Earth navigation controls can steer the camera through the front door of the newly renovated Reichstag and into the chambers of the German parliament.

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But a true mirror world shouldn’t be static, as the Berlin model and the Darfur layer are; it should reflect all the hubbub of the real world, in real time. As it turns out, KML also supports direct, real-time exchanges over the Internet using the hypertext transfer protocol (HTTP), the basic communications protocol of the Web. One hypnotic example is the 3-D flight tracker developed by, a company that offers online flight-planning tools for general-aviation pilots and enthusiasts. Download the KML layer for one of the eight major U.S. airports that Fboweb covers so far, and tiny airplane icons representing all the commercial aircraft heading toward that airport at that moment will be displayed at the appropriate altitude in Google Earth [Google Earth link]. As time passes, each flight leaves a purple trail recording every ascent, turn, and descent, all the way down to the runway. It’s a plane-spotter’s dream.

Microsoft, as one might expect, isn’t far behind Google in its effort to bridge map worlds and the real world. Scientists at Microsoft Research are perfecting a system called ­SensorMap that collects live data from any location and publishes it in Windows Live Local (the latest name for Microsoft’s online 2-D maps) or Microsoft Virtual Earth. Researchers at Harvard University and BBN Technologies in Cambridge, MA, won a grant from Microsoft this spring to create a SensorMap interface for “CitySense,” a network of 100 Wi‑Fi-connected weather and pollution sensors they’re installing in Cambridge. Other scientists, however, are already using Google Earth to monitor live sensor networks. At the Center for Embedded Networked Sensing at the University of California, Los Angeles, researchers have connected a network of wireless climate sensors and webcams in the James Reserve, a wilderness area in California’s San Jacinto Mountains, to a public KML layer in Google Earth. Click on an icon in Google Earth representing one of the reserve’s nest boxes, and you get a readout of the temperature and humidity inside the nest, as well as a live webcam picture showing whether any birds are at home [Google Earth link].

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