The next time you see Milwaukee Mayor Tom Barrett, ask him about his map. It’s the Mayor’s latest weapon in his battle to stop the state from eliminating residency requirements for municipal employees in Wisconsin. More than 120 municipalities have rules spelling out where their employees can live. But Governor Walker wants to change that. He says residency requirements are unnecessary and outdated, even counter-productive, and he has included language in his state budget that would end them.

Mayor Barrett says the Governor’s proposal doesn’t belong in the budget, since it’s not a fiscal item. But Barrett’s concerns go much deeper. In a recent e-mail to supporters, Barrett said an end to the city’s 75-year-old residency requirement could “destabilize” Milwaukee. I pressed the Mayor on that claim in a recent television interview. He said philosophically he agrees with the notion that people should be able to live where they want, but that local municipalities should be able to determine the conditions of employment for the people they hire. In Barrett’s world, that translates into a simple reality. If you don’t want to live in Milwaukee, don’t apply for a job with the city. He said there’s been no shortage of applicants.

Perhaps more important, Barrett said the value of assessed property in Milwaukee had fallen five billion dollars because of the economic downturn. He argued that based on experiences in other cities, such as Detroit, Minneapolis, Baltimore, and Cleveland, significant numbers of city employees were likely to leave the city should the residency requirement be lifted. Barrett was making the case that there was great risk to his city, and he wanted to show me a map he carried with him into the television studio. You can see it here. Because of the amount of data in the file, it takes about 10-15 seconds to present itself.

The map shows the gravity of Milwaukee’s foreclosure crisis. Foreclosed properties are in red. As of last week, there were nearly 2600. Blue represents where the more than 7,000 city employees live. Besides helping stabilize struggling sections of Milwaukee, city employees are the backbone of a number of healthy, middle-class neighborhoods, including Bay View and the southwest, far south, and far west sides. These neighborhoods are home to hundreds of police officers and firefighters. But what happens if, as the Mayor believes, 40 to 50 per cent of those blue dots—city employees—move outside the city? Will there be a dramatic downward pressure on property values?

The Mayor contends the end of residency was a promise Governor Walker made to the Milwaukee police and firefighters unions in an effort to gain their support during his bid for Governor. Walker argues that personal freedom should trump conditions of employment, and that at the end of the day, it’s up to the city to become a more attractive place to live. Neither man knows exactly what will happen should the requirement be eliminated. Nor do they know what Mayor Barrett’s map will look like 10 years from now. But if Barrett is right, it will be a lot less blue, and Milwaukee could be a very different city.