First, it was Youngstown Mayor Jay Williams calling for his town to shrink its service area to fit its smaller population. Then it was Harvard professor Ed Glaeser last Friday advising Buffalo to do the same. And now Detroit Free Press deputy editorial page editor Stephen Henderson is admonishing Detroit to fall in line and recognize a new reality: 139 square miles for fewer than a million people is just too big. Henderson put it bluntly. "Here's the stark truth, unpopular as it may be. To survive, Detroit has to get smaller. Way smaller -- as in more compact and efficient, and less strained to provide services across a sprawling, 139-square-mile landscape with a population density that is, on average, less than half what it was 50 years ago," he wrote. "We tend to talk about Detroit's dramatic population loss in terms of raw numbers -- the popular obsession with rankings and the magic sense of urban identity associated with having a million or more residents. [But]"...Detroit's troubles are as much about losing density as they are about losing people. "In 1960, when Detroit had more than 1.6 million residents, 71% of the city's census tracts had 10,000 or more people per square mile; only 6% held 5,000 or fewer per square mile. "But by 2000, when the population had dipped just below 1 million, 20% of the census tracts had 5,000 or fewer per square mile, the kind of density you see more frequently in suburbs. Only 23% of the city had 10,000 or more people per square mile." And then he gets to the punch line: "So as the city lost people, huge swaths of Detroit also lost the kind of residential density that generates the tax revenues needed to support services across such a huge geographic area. The result is city resources that are just stretched too thin to be effective." Henderson raised the provocation far more urban leaders should be asking. "If there are only two houses on [a] block, the city still needs to police it. A fire station still must be within a reasonable distance. And fixed infrastructure costs -- lighting, sewers, street paving and the like -- don't change much. And now the taxes generated by those two houses don't come close to covering service costs." Good for Stephen Henderson. The question now is how to do it.