Using technology to make cities better.

That's the theme of the 2013 Mayors' Innovation Summit. It's the work of the U.S. Conference of Mayors, of which Philadelphia Mayor Michael Nutter is current president.

After opening remarks Thursday morning, the two-day conference turned to one of Philly's burgeoning strengths: open data.

"That's what happens when you have a lot of people in cities looking at information — they come back and show you things you hadn't even thought of," said Sly James, mayor of Kansas City, Mo.

To James, open data is all about transparency. That's all well and good, says John Tolva, the chief technology officer of Chicago. But Tolva — who sat on the "Creating Data Democracies for the Public Good" panel — wanted to make sure the mayors knew that open data is about more than just sunlight.

"It becomes a platform externally for a sort of innovation ecosystem," said Tolva, "for people to build applications — and businesses in some cases — on top of these vital signs that we're publishing."

He mentioned a new "predictive analytics platform" that Chicago recently won $1 million to developThe idea, Tolva says, is to crunch public data to see the likelihood of a block falling into blight, for example, or the impact of an added lane of traffic.

Tolva says the plan is to make that technology available to other cities as well. "Because the value of a tool like that becomes exponentially greater when we're able to say, 'Why did that work in Philly but not in Chicago?'" he said.

The emphasis on sharing was echoed by Philadelphia's chief data officer, Mark Headd, who says open data success is contagious.

"Every time I see these cool things that Chicago's doing, I'm scheming about how we can do those things in Philadelphia," Headd said.

Chicago's Tolva put it differently: "The rising tide of data lifts all boats."

That ethos of comparing notes and "stealing" ideas speaks to the broader goals of the tech summit.

Thursday featured a full slate of panel discussions on topics ranging from broadband infrastructure to seeding civic engagement. It concluded with an evening tour of the Navy Yard and a reception at Urban Outfitters.

The gathering of 30 U.S. mayors — and dozens of city officials and business leaders — wraps up Friday afternoon.