Greater Boston could stagnate and become a far less vibrant area over the next few decades, choked by restrictive housing policies that help drive away restless young people and leave behind a rapidly aging population.
Or it could boom, driven by a surge of young adults drawn by affordable housing and the appeal of urban areas that offer exciting cultural and entertainment options, top-notch colleges, and smart transit choices.
These competing visions were laid out in a report released this month by the Metropolitan Area Planning Council. Which scenario plays out, planners say, depends on housing and transportation decisions that are being debated in many cities and towns right now.
“If we don’t have the housing we need, we can’t attract the people we need, and it discourages employers from moving to the region,” said Marc Draisen, executive director of the regional planning agency.
If there is strong growth, a large number of communities would see their population expand, some substantially, according to the report. Boston’s population could shoot from 617,000 in 2010 to more than 700,000 in 2030, with nearby urban areas also expecting growth, it says.
Among area communities, five — Ashland, Bedford, Brookline, Shirley, and Upton — are projected to grow 15 percent or more. But 12 are projected to shrink, with the list including Lincoln, Medfield, Millis, Sherborn, and Wayland.
The region will see strong growth if it can build enough housing, particularly apartments and condos in urban areas and town centers, if it can attract and retain more young people, and if the trend toward urban living continues, according to the report.
On the other hand, “continued widespread opposition to new housing” will likely result in less growth, the report’s authors said.
The Boston metro area, which the MAPC report defined as encompassing about 160 communities roughly within the Interstate 495 belt, could grow by more than 12 percent, to about 5 million residents, by 2040 if there is strong growth, or by about 6 percent if growth is slow.
Draisen pointed out that the numbers are simply projections. Communities could grow or shrink at rates not predicted because of policies and decisions taken by local officials or other changes not accounted for in the report.
Draisen cited Natick as an example of a community that is planning well for growth.
Timothy G. Reardon, the Metropolitan Area Planning Council’s assistant director of data services, said Natick stands out demographically from some other suburban communities because younger people — ages 25 to 40 — are moving in, which is good because “young adults are critical . . . to grow the economy.”
Josh Ostroff, a selectman in Natick, said his board, the Planning Board, and Town Meeting members “have been supportive of development that is accessible and connected.”
The town has worked hard to promote more affordable and diverse housing, through working with developers and by embracing “smart growth,” which emphasizes denser housing near public transportation and retail districts.
Development is growing especially around Natick Center, where there is a commuter rail stop, Ostroff said, citing the renovations of a century-old structure into a small apartment building and a former paper recycling plant into 150 housing units.
The town is also studying how to make the commuter rail station more accessible, and how to integrate it better with local bus lines.
Companies are interested in towns that provide good transportation, good schools, and recreational opportunities, and respect the need for open space, Ostroff said.
“If we want Massachusetts to be the first choice for employers and employees, we need to provide adequate means to get to work,” he said.
The region faces staggering demographic changes over the next few decades as members of the baby boom generation retire, said Draisen. Younger people will be needed to take their places in the workforce, and to help the region grow, he said.
Housing is key, said Draisen. Employers want to start companies in the area and employees want to live here, but housing prices are so high it is difficult to find anything priced within reach of younger workers Especially needed are affordable homes in urban areas and around town centers, whether they are apartments, condos, or single-family houses built on small lots.
The report says about 435,000 units of housing will be needed, primarily in urban areas and mostly apartments and condos, for both young people starting out and older people moving out of single-family homes.
Younger people are far more interested in living in areas where work and entertainment are close at hand, even within walking distance — a much different attitude from that in the 1960s and 1970s, when homes were built far from major employers, Draisen said. Increasingly, people hear the term “bedroom community” as a negative, a reversal from a generation ago.
He does see communities where officials understand this, and cited Boston, Cambridge, Somerville, Chelsea, Salem, Quincy, Malden, Melrose, and Natick as examples.
It doesn’t have to be just the big cities that grow, he said. Young people want to be in town centers where there is good mass transit and entertainment, “where there’s vibrancy and lots of things going on.” They don’t mind having a car, but don’t want to drive everywhere.
He is optimistic about growth, but change can be difficult. Municipal officials may understand what needs to be done, but “the gap between understanding and zoning, that will be a big challenge.”
Many developers still find themselves tied in knots over projects that should be allowed to move forward quickly, he said. Communities need to be more proactive and allow more building in the right places. The region now builds about 8,000 units a year; that should be as high as 14,000 to meet future needs, he said.
Barry Bluestone, director of the Dukakis Center for Urban and Regional Policy at Northeastern University, praised the MAPC report as showing a path forward for Boston communities. And he echoed the report in noting that its conclusions are only projections, and communities can make changes to shape their future.
The three most important issues are affordable housing that’s appropriate for young people, such as apartments and condos in city or village centers; good schools; and fun, interesting amenities such as good restaurants and parks. Mass transit is also needed, he said.
“Demographics are not destiny,” he said. “They can change their destiny.”
But if changes are not made, the metro area could become much older and less vital, he noted. What is needed, Bluestone said, is “putting in place programs and policies that allow the region to grow faster, and retain and attract younger people.”Matt Carroll can be reached at email@example.com. Follow him on Twitter @globemattc.