40,000 city properties. Abandoned. Now what?

Philadelphia hasn't suffered the same population loss as Flint - where much of the abandoned land is being converted into gardens and open space. But Philly's population has dropped from just more than 2 million in 1950 to about 1.5 million now. Yet the city's 1960 comprehensive plan was based on the notion that the number of residents would grow to 2.5 million.

"The city is much smaller than it was built for," Hughes said. "There are huge amounts of city that it doesn't make sense to build on. We don't need this physical city to be capable of housing 2.5 million people any more."

And some experts stressed that while a land bank might be a helpful tool to improve vacant-land management, it won't suddenly make all these properties desirable to investors.

"The overwhelming majority of the properties that get registered to a land bank, there's going to be no buyer for that," Hughes said. "The vast majority of parcels that enter the land bank, it's not going to be selling the land, it's going to be managing them while vacant."

Still, former City Housing Director John Kromer said now is a good time for the city to get property plans in place, before the economy rebounds.

"One important thing to remember about vacant properties is, as we emerge out of the recession, more and more people are going to realize how valuable they are," Kromer said. "I think it means that investors and developers that previously hadn't looked at Philadelphia would take another look."