Two years ago, Robert Cheetham applied for a $90,000 government grant built around a question as old as the practice of urban planning: What can a tree do for a neighborhood?

Sounds simple. But Cheetham's analysis digs into storm-water management, carbon sequestration, heat effects, "even real estate value," he says.

Those queries make up the core of PhillyTreeMap, a recent project of Cheetham's company, Azavea, a Philadelphia-based software-engineering business specializing in geographic data analysis.

Launched in April, the digital map (viewable at PhillyTreeMap.org) is a wiki-construct, meaning that, like the crowd-sourced online website Wikipedia, the map is only as accurate as its users. Anyone who joins the site can post the location and species of a tree - say, the one in your backyard.

So far, more than 144,000 trees in the city proper appear on the map - neon green dots lining the urban grid. Click on one, and you'll get information on trunk diameter, height, and "yearly eco impact," a service that aims to tabulate the dollar value of each tree in terms of environmental benefits such as greenhouse-gas reductions and water usage.

"Before this, people were kind of doing [tree counts] on their own, and there wasn't a central mechanism for them to be in one place," says Patrick Morgan, Philadelphia Parks and Recreation spokesman. "This is a great tool for people to see how their contributions will, over time, help the urban forest grow, which I think is pretty cool."

Morgan hopes the tree map encourages people to plant trees, as much as count existing ones. Proactive planting from residents is what Mayor Nutter's "GreenPlan" effort needs to reach its goal of 300,000 trees in the ground by 2015, Morgan says. The plan is part of Nutter's Philadelphia Greenworks initiative, which seeks to make the city "the greenest in America" in less than five years.

So far, trees and vegetation cover about 17,000 of the city's roughly 88,000 acres, or about 20 percent, Morgan says. About half of the city's total acreage can accommodate vegetation, he says.

PhillyTreeMap took root on the back of a research grant for small-business innovators that Azavea secured in 2010. Cheetham says Azavea took cues from OpenStreetMap, a global mapping endeavor based in Europe, and worked in concert with Urban Forest Map, a similar geomapping project in San Francisco.

Now, Cheetham is waiting to hear back on a follow-up grant Azavea is vying for that would go toward creating mobile apps and rolling out a reputation aspect for users on the website. Essentially, people who reliably input good data would receive elevated user status that would grant them more editorial control of the map.

"We want to incite people to compete against each other and track scores for particular neighborhood groups," Cheetham says. He expects to hear back on the grant in September.

Another possible addition to the tree map would incorporate social media, allowing users to announce to the online community that, say, they watered a specific tree or grove on a certain date and time.

Cheetham's grand vision for the tree map is to create a digital environment that educates people about urban ecosystems and informs city planning projects. In July, Azavea released the source code for PhillyTreeMap.org - under the name OpenTreeMap - which basically means the map can be altered to fit any city or community, not just Philly.

"This," Cheetham says, "is something that can be applied to any city in the world."