Emerging Technology: Keyhole

In the canon of great nerd party tricks, this one stands out: I invite a friend to sit down in front of my computer monitor, where a 3-D image of Earth floats against a black sky. I hit a key, and a virtual camera slowly begins to zoom in. First the broad outline of North America becomes visible, then the ragged coastline of the northeastern seaboard. The image grows sharper, revealing undulations of topography—the gentle slopes of the Adirondack Mountains, the miniature fjords along the Hudson north of New York City—and a gray mass of urban sprawl.