Somewhere in the hills of Merom Bluff Park in Indiana, up above the Wabash River, sits an ammo box filled with bric-a-brac: old Frisbees, rubber money, toy dinosaurs, key chains. Odds are that in the next few weeks, someone armed with an advanced Global Positioning System (GPS) device will attempt to find this box. Not because it holds anything of value. In fact, the explorer who tracks it down will end up swapping a few items and leaving the box where it is. Such are the rules of the curious new pursuit known as geo-caching: Someone puts a few trinkets in a box somewhere and uses the Web to publish the GPS coordinates (latitude and longitude) that tell where the cache is. Intrepid geo-cachers will then use their tracking devices to find the box, dutifully remove a few items, and contribute a few new ones of their own.
"I don't go out looking for the goodies; the joy is in the hunt for the cache itself," says Ed Hall, a software engineer who in his free time maintains a Web site devoted to the pastime. "Discovering what's there and enjoying the views along the way, that's why I go geo-caching." Hall's Web site (www.brillig.com/geocaching) features updated maps of thousands of known caches, many of which have been visited by dozens of cachers. (Hall himself has located more than 300.) It's one of those great if slightly loopy milestones of modern technology. Decades of research and $12 billion worth of satellite hardware, and what do people do with it? They use it to locate the sort of treasure you'd find in a cereal box.
And that says something important about GPS. Those maps on Ed Hall's site are definitive proof that GPS has reached critical mass in terms of mainstream adoption: The technology is now being used in ways its creators never imagined. Originally designed by military engineers to help smart bombs home in on their targets more effectively, GPS has until recently found its primary consumer application in the clunky onboard navigation systems of luxury sedans and SUVs. But the information captured by the GPS system—location, location, location—is universal enough that new uses were inevitable. Geo-caching is fun, but the most intriguing new applications of GPS may end up transforming everyone's sense of physical space. What if you think of GPS as a kind of 3-D version of the Internet, a hypertext Web spun out in real-world geography?
GPS is based on the fundamental geometric principle of trilateration: If you know your distance from three distinct points, then you know your exact position on a map. (If you're interested in altitude as well, you need four points.) GPS receivers coordinate with a system of 24 satellites maintained by the Department of Defense. Because these satellites follow predictable orbits, their exact location at any given time is easy to determine. A GPS receiver in your car or on your personal digital assistant (PDA) receives radio signals from satellites overhead and gauges its distance from each satellite by calculating how long it takes the signals to arrive. Before 2000, the military deliberately scrambled GPS signals for consumer use to limit the precision of location readings. However, today the accuracy range of ordinary receivers is typically 30 feet. (Some high-end models, using several frequencies, can generate accurate location readings to within a foot.)
Of course, the ordinary user sees only the end result of this complex interaction, which is a string of digits representing latitude and longitude. In the case of the Indiana ammo-box cache, the coordinates are 39°03.515' N, 087°34.173' W. This is a unique identifying number for a particular point on the planet. Wherever you go, there is a set of longitude and latitude coordinates that describe your exact location. This observation might seem self-evident, but it connects in a crucial way to the founding unit of the World Wide Web: the URL, or uniform resource locator. Just as every point in real-world space has a GPS tag associated with it, every point in information space has its own unique address. The key to mass adoption of the Web was that anyone could attach information to a given address and know that this information could be accessed from any Web browser anywhere in the world.
The great breakthrough on the GPS horizon lies in thinking of those geographic coordinates as a real-world URL. In other words, think of those digits not simply as a description of a point in space but as a place to store information. Today you can create a Web address and publish pages and pages of anything you want there. But soon you'll be able to take a GPS location—say, 40°43.833' N, 073°59.814' W, the coordinates for Washington Square Park in New York—and publish material there as well. Anyone walking through the park would then be able to browse through the data you've uploaded. Some of this information might be targeted at a general audience and include recommendations for nearby restaurants, or a public bulletin board for discussing improvements to the park itself. But the messages stored might also be more personal, such as diary entries stored at the very place where the events described in the diary occurred, a kind of first-person geo-cache. There might even be bits of text targeted at a specific person, like an e-mail message floating in space, waiting for its recipient to come into range and receive it.
IBM researcher J. C. Spohrer, who helped concoct an early prototype for a GPS-based hypertext called WorldBoard, describes this kind of system as a "planetary chalkboard." I prefer to think of it as a kind of graffiti that makes an environment more habitable and socially connected.
Attaching digital information to physical spaces has until now been largely associated with prepackaged tourist guides offered by such services as Vindigo. The model is intuitive enough, if not terribly imaginative: A company licenses restaurant reviews and shopping guides from a travel publisher and creates a system in which users can download relevant information to their PDAs or laptops as they roam through a city. Such services are useful, but the prepackaged content limits their scope. When I hear evangelists talk about these digital tour guides, I'm reminded of the early 1990s hype about "hypermedia" CD-ROMs and the digital revolution. The digital revolution did eventually go mainstream, but it ended up happening elsewhere—on the Web, precisely because the Web made anyone a potential hypermedia publisher. The planetary chalkboard will become interesting only when ordinary people can pick up a piece of chalk and write something.
"Instead of having just tourist information, the system would be open," says Swedish researcher Fredrik Espinoza, cocreator of an experimental tool called GeoNotes. "There would be much more social activity." Espinoza's vision includes a filtering system for retrieving GeoNotes that have been posted by friends or other trusted sources, like the buddy list of Instant Messaging. Imagine, for instance, that you stumble across a beautiful side street in a historic district, the sort of urban discovery you might tell your friends about the next time you meet them for coffee. With GPS-based hypertext, you could leave a virtual note hanging near the street, addressed to your 30 closest friends. The next time they happened to stumble through the area, the text would pop up on their PDA screens: "Hey, come check this out ... "
Annotatespace.com creator Andrea Moed sees potential in this for a new kind of storytelling. She has created a walking tour of New York's vibrant new bohemian neighborhood, Dumbo, short for Down Under Manhattan Bridge Overpass. The project is more performance art than tourist guide. "I wanted to create a model for location-based content that went beyond the basic 'What is there to buy here?'" Moed says. "When you can stand where others have stood and learn how it affected them, and then share your own impressions in return, public space becomes more deeply public than it was before."
William Gibson, the sci-fi writer who coined the term cyberspace, once wrote: "The street finds its own uses for things, uses the manufacturers never imagined." His words are inevitably rolled out when describing some unlikely new grassroots application of an existing tool, like geo-caching. But software such as GeoNotes or WorldBoard suggests a further twist: The street finds new uses for the street itself. Simply strolling down the sidewalk can become a hypertextual exploration, a journey into a new information space layered over the real one. Suddenly the surrounding air is full of information—some of it created for you by your closest friends, some of it created by total strangers. The streets are alive with data.