"Hydra-bus!" by Michael Wallace (Michael Wallace / June 28, 2012)

Like a bee doing a waggle dance to signal a field full of pollen, or a cat rubbing up against a fence post to make a scent chart of its territory, GPS artist Michael Wallace maps out a virtual Baltimore during his bike trips around the city.

Using a global positioning system tracking application on his cellphone, the 40-year-old Baltimorean "sketches" elaborate scenes that are superimposed on maps of city streets.

He has drawn Godzilla battling Mothra, the lunar landing, the sinking of the Titanic and a horse running at the Preakness. There's even a rendition of a gun-toting stickup man modeled after Omar, Wallace's favorite character from the HBO television series "The Wire."

After he finishes each ride, Wallace downloads his route/drawing onto his website, wallygpx.com. It's a process that he describes as virtual graffiti, because he can express himself freely without defacing public property.

"It's like digital spray-painting," Wallace says. "Wherever I go on my bike, I leave this invisible line behind that exists only in the ether."

By profession, Wallace is a middle-school geology and earth science teacher. He doesn't aspire to be the next Andy Warhol or Roy Lichtenstein. But when he explains why he devotes so much time to his drawings, he expresses himself in terms familiar to any artist.

"There's so much mystery out there," Wallace says. "When I start, I never know what I'm going to bump into. If a fence or a tree is in the path line of a drawing I'm trying to make, I have to notice it, react to it and be a part of it."

Wallace is one of the better-known practitioners of the art form. He's given interviews to newspapers, radio and television stations in Baltimore, Washington and Great Britain, and he says that about 80 percent of his roughly 300 Twitter followers are European.

His drawings may be popular because they're playful. They're also detailed and complex and reveal a genuine knack for drawing. Not just any cyclist with a map and cellphone could produce them.

Though he doesn't sell his work or accept advertising on his website, a few of his framed and signed drawings can be found in taverns nearby his Canton rowhouse, including the Laughing Pint and Elliott's Pour House.

Rebecca Hoffberger, founder of the American Visionary Art Museum, says that GPS drawing is an example of the human impulse to find hidden structures underlying seemingly random pathways.

The same urge can be detected in sources as different as the "Family Circle" cartoon strips tracing little Billy's circuitous route to the mailbox and the Nazca Lines made by ancient Peruvians. The latter — giant, stylized images of squirrels and hummingbirds made by removing pebbles to expose the ash-colored soil — can be seen in their entirety only from an airplane or mountaintop.

"These kinds of art make us more conscious of where we leave our footprints behind," Hoffberger says. "It's a very lovely and poetic thing to do."

GPS art has been around since at least 2000, when a British artist named Jeremy Wood began using his device to record the shapes of his commercial airline flights and holding patterns. From there, Wood wrote in an email, he began turning on his GPS and tracing his route every time he left his house in Oxfordshire, whether he was on foot, riding his bike or inside a boat.

Museums began collecting Wood's drawings, and eventually he branched out into more experimental carriers, attaching the device to a lawn mower and to dogs to find out where they roamed. One canine let loose in a field, he wrote, "drew the head of a dog."

In 2003, The New York Times listed GPS art as one of the upcoming trends in the art world. But because the practice combines technology, exercise and drawing, it can also be a form of recreation.

For instance, a Spanish graphic designer named Joan Pons Moll has invited visitors to his website to take part in a collaborative project he's called "Running Alphabet." He and his volunteers will jog each of the 26 characters while carrying a GPS, and create a typeface from the results.

In Portland, Ore., a group GPS art project was held in 2010 and 2011 as part of Pedalpalooza, the city's annual, three-week bike festival.

Some GPS artists noted that because American cities such as Baltimore are laid out in grids, they tend to produce hard-edged drawings that include lots of rectangles and squares.