IMAGE: GLOVENTURES

It's a drizzly Sunday in Marymoor Park, a leafy hangout for soccer kids and Ultimate Frisbee jocks, in Redmond, Wash. This afternoon, however, a new breed of outdoor enthusiasts has taken to the field.

A half-dozen people are wandering the grounds while holding their cellphones at arm's length. They move in urgent and idiosyncratic trajectories, shifting directions on the fly without peeling their eyes from their phones. For the drivers on the highway nearby, it is an unusual sight: a group of oddballs apparently roaming in the rain for reception [see photo, "Off the Couch"]. But, in fact, the wanderers are not muttering, "Can you hear me now?" They're playing Raygun.

The conceit is that you're hunting for ghosts. The phone displays a sort of supernatural radar screen that tracks surrounding ghosts as tiny colored dots. The object is to gobble up the dots before they get you. In a way, it's a little like Pac-Man, but with one key difference, as James Robarts of GloVentures LLC, in Redmond, Wash., the developers of the game, puts it: "The joystick is you."

Raygun is one of the first so-called location-based games. Played with a mobile device such as a cellphone or a PDA, it uses Global Positioning System (GPS) technology to transform the real world into a virtual arena. It's a video game that can actually make you sweat.

It also represents the bleeding edge of a bleeding new culture and industry: mobile games, which brought in US $72 million in the United States in 2004 and are expected to boom to $430 million by 2009. So far, most mobile games have been Lilliputian approximations of the stuff players find on a PlayStation or a PC—Tetris, video poker, and the like.

Location-based games are boldly going where no games have gone before: to the cold, wet fields of reality. They aim to transform not only the way people conceive of electronic games but the way they experience them.

"We're big fans of the real world," says Robarts with a grin, as rain drips from his cap on the sideline of the Marymoor field. "Our goal is to get gamers out into it."

"Let's go out in the cul-de-sac and play Snake!" Robarts exclaims, as he grabs his Pocket PC. It's a few hours after the rainy Raygun play out in the park, and we've retired to his house. But now the clouds over Redmond have parted to reveal a picture-perfect day. And he's going to enjoy it in the way he likes best: playing a location-based game.

Robarts, a lanky 47-year-old, stands in the center of the street and boots up his handheld. The game is a GPS version of the popular video game Snake, in which the player must navigate an ever-elongating reptile around a series of obstacles on-screen. Easy to learn but difficult to master, the traditional version of Snake has become an evergreen title for both cellphones and PCs. But no one has played Snake quite like this.

When Robarts activates the game, the software displays geographic coordinates that act as the boundaries and obstacles of the game. The Pocket PC, which includes a GPS chip, keeps track of Robarts's position. Every few steps he takes—roughly every second—the change in position is logged, and the image of the snake on the Pocket PC screen is refreshed. So instead of wiggling a joystick to maneuver the serpent, Robarts simply has to maneuver himself. He demonstrates by jogging in a broad arc, and his snake follows along. "I do this twice a day," he says, between breaths. "It's my aerobics!"

Robarts's title at GloVentures is director of dreams, and his dream of location-based games has been a long time coming to fruition. "Innovation is my life," he says. As an Eagle Scout in the 1970s, Robarts participated in the U.S. government's Mentally Gifted Minors program, a Cold War project meant to train future rocket scientists. Later, while working on creating guidance systems for cruise missiles, Robarts learned a valuable lesson for any aspiring engineer. "Problems don't get solved by a bolt from the blue," he says. "You have to deliberately work through them to get to the magic."

That understanding served him well during his early work on location-based games. After stints at various jobs, including one at Microsoft's Advanced Consumer Device Group, which was working on moving the Windows operating system from the office to the living room, Robarts joined a start-up devoted to wearable computing. The software the company developed included a tracking element, which Robarts thought might have entertainment applications. So he took his co-workers to Mexico in 1999 to test out what he loosely calls "a GPS-aware travel guide wrapped in a scavenger treasure hunt."

Though fun, the high-tech road rally revealed an inherent challenge of location-based games: latency. Because the software relies on triangulating the faraway GPS satellites for tracking, the action is not in real time. Today, even with the GPS chip set being monitored every second, there's still a 5- or 6-second delay before changes in position show up. Rather than fight against the technology, Robarts and his team chose to incorporate that into the challenge. "You can't turn without experiencing lag," he says, "so that's part of the game."

In 2002, Robarts and Cesar Alvarez, a former colleague from Microsoft, launched Glofun as a division of GloVentures to pursue this new form of gaming full-time. Instead of the scavenger hunts Roberts had tried in Mexico, the team explored more narrative-based games, which Robarts describes as "Myst in the real world." Myst, one of the best-selling games of all time, allows players to explore a fantasy world and solve intricate puzzles.

In Robarts's version, locations would be pinpointed on the GPS system so that when the gamer arrived there, the device would display clues, dialogue, or character information. For example, a player might wander out into the woods to find a ghost at one location, whose story would lead to another location.

As in the pioneer days of PC gaming, Glofun's early experiments were rife with mishaps and misadventures. Misplaced navigational points had some intrepid gamers literally wading out into Seattle's chilly waters, with their Pocket PCs hoisted high above their heads. "We were crossing streets of traffic," Robarts recalls, "and we said, 'This is bad.'"

To avoid broken limbs or worse, Glofun reduced the boundaries of the games to something more manageable, such as a soccer field. The company relies on the GPS chip set built into certain phones, such as the Nextel i710 and i730.

The effect fulfills Glofun's goal of blurring the line between fantasy and reality. "We like ghosts [in our games]," Robarts says. "It's a rich narrative device. These things could be around you, but you're not aware of it." That is, until you pick up the phone.