Here’s one way to put Chicago’s demographic problem: Since 1950, the city has lost more people than currently live in all of San Francisco, Boston, or D.C. After finally increasing its population in the 1990s, the 2010 Census found that Chicago – unique among the large, relatively prosperous cities we consider our peers – had declined by 7%, or around 200,000 residents.

Indeed, just a couple miles from the heart of the Loop lies a neighborhood that, despite a rich history, beautiful architecture, and quick access to the second-largest business district in America, has lost 40% of its population since the middle of the last century. An area that once held 102,000 people is now home to barely 64,000.

That area is called Lincoln Park.

For a long time, most accounts of Chicago’s lagging population have focused on parts of the South and West Sides where many residents, largely African-American, have decided to decamp for the suburbs or the South in search of better schools, less crime, and more jobs.

But the under-appreciated flip side of population loss in those parts of the city is that places that ought to be growing like gangbusters are stagnant, often sitting 25% to 50% below their peak populations. Lakeview, for example, was once home to 124,000 people; its population is now 94,000. North Center is down from nearly 49,000 to under 32,000. West Town, which includes Wicker Park and Bucktown, has fallen from 187,000 to 81,000.

Compare the maps: many of Chicago’s wealthiest neighborhoods are dramatically below their peak populations.

Even more startling, these areas aren’t necessarily gaining back those people. Lincoln Park, Lakeview, and North Center all actually lost population in the 2000s. Logan Square, whose rapid ascent as a “hot” neighborhood picked up steam during that decade, was home to 11% fewer people in 2010 compared to ten years earlier.

The problem, obviously, is not that people don’t want to live in these neighborhoods. Home prices and rents have skyrocketed over the last ten to twenty years; average incomes have climbed with them, as more and more of the well-to-do decide Chicago’s North Side is a place they’d like to call home.

So what’s going on? And why should we care?

One reason is that over the last few generations, Americans all over the country have spread out a bit: apartments that used to hold a family of five or six now contain a family of three or four – or maybe a childless couple who have turned a bedroom into an office. Or maybe just one person, living alone. This is especially true in wealthier areas, where people can afford to buy themselves more space. As a result, if a neighborhood has roughly the same number of housing units it had fifty years ago, it probably has a significantly lower population.

But that doesn’t explain why these neighborhoods, which have become so popular, haven’t seen the construction of more housing units. For most of Chicago’s history, when a neighborhood became more popular, builders created more housing, turning houses into three-flats, and three-flats into courtyard buildings. In a few really high-demand areas, like right along the lakefront or near downtown, they might even have built highrises.

But for the last several decades, increasingly strict zoning laws have outlawed this kind of gradual build-up. Instead, Chicago’s laws allow a massive boom in parts of downtown – mostly where there weren’t enough white-collar residents to complain – while putting a tight lid on the neighborhoods.

Since replacing a couple two-flats with a courtyard building is now illegal, developers make money by tearing down an old two-flat and building a luxury two-flat in its place. Or they build a mansion, and the neighborhood actually loses a housing unit. As a result, as a neighborhood becomes more attractive, the city encourages fewer people to live there.

And that’s how we arrived at the bizarro-world reality that Lincoln Park actually lost roughly the same number of housing units as Englewood between 2000 and 2012.

You can see how dramatic the effect is by looking at population growth around the borders of downtown: where relatively loose downtown zoning holds sway, the number of residents boomed. But instead of gradually tapering off as you get further away, there are sharp drop-offs all around the central area. Often, a few blocks where the population grew by 50% or more are right next to a few blocks where population actually declined. In most cases, zoning plays a crucial role in those disparities.

But so what? Why does any of this matter?

For one, it matters because if the number of housing units in a neighborhood is capped, as that neighborhood becomes more desirable, affluent new arrivals will outbid existing residents and people of moderate income, pushing up housing prices and creating newly segregated enclaves. If we want regular people to be able to live in some of our safest, most transit-accessible neighborhoods, allowing the supply of housing to grow with demand is a crucial part of that affordability.

Second, as places like Lincoln Park become forbiddingly expensive, some people decide their next best option is, say, Wicker Park or Logan Square. When they arrive, they open coffee shops and hipster bars, attracting people with more money, who then bid up housing prices there, expanding the parts of the city where the working class simply can’t afford to live.

But most potential residents will just decide to move to the suburbs. And, once there, they won’t be supporting neighborhood businesses. They won’t be contributing to the city’s tax base. In other words, by pushing people to the suburbs, we’re giving up neighborhood jobs and money the city desperately needs to provide services in every neighborhood in the city, including – especially – the ones that are actually struggling, far from Lincoln Park.

The fact that Chicago’s affluent North Side communities have lost so many people, and aren’t gaining them back, is a huge problem for many local businesses, current residents of moderate means, and anyone who would like to move there but can’t afford to.

But even if none of that describes you, it’s also a problem for those of us who’d like to see City Hall have more resources to invest in other parts of the city, from policing, to schools, to transit, to road repair. It’s a problem for those of us who’d like to see more jobs created within commuting distance of Chicago communities where unemployment is endemic. It’s a problem, in other words, for all of us.