The large numbers Talmage speaks of translated in Washington, D.C., into the finding that "we were losing around $1.2 billion in sales tax to Virginia and Maryland," Stevens says.

In city after city, the words of Federal Reserve Board Chairman Ben Bernanke have been borne out: "Free markets can be a powerful source of economic development, but markets work less effectively when information about potential opportunities is absent or costly for private actors to obtain." That comment was made in an April 2006 speech that noted the work of Social Compact.

The Social Compact Web site contains Neighborhood Market DrillDown data for areas of cities under study, with the mission to make data widely and easily available. The objective in Detroit reflects what has been done with other cities that are more along the way in using the data -- Savic says that the idea is that retailers and developers will be able to find data at the Web sites of Social Compact or the city on their own, "so that we can just spur that market."

For the cynics among us who see development as primarily the opportunity for retail monoliths to make a buck, Talmage notes that direct links have been shown between obesity and diabetes in areas that have no full-service grocery store. Some of us may well find it hard to imagine a place where there isn't such a store within easy distance, but grocery stores operate on thin margins and so tend to be much more conservative in their site selection than other retailers.

"We've been able to use data to work with Winn-Dixie in Miami, for instance, or Giant Foods in Washington, D.C., to look at underserved neighborhoods," he says. "These neighborhoods can support that investment. They have a large enough customer base and discretionary income."