Cities represent the future of humanity — and that means we must figure out how to make them more livable. The share of people who live in urbanized areas more than doubled in the US and across the world from 1900 to 2000. More than eight in 10 Americans live in cities today, as do the majority of people worldwide.

These densely populated places have created tremendous opportunities for innovation, economic growth, more efficient infrastructure and transit, and the curation of arts and culture. But the density that gives cities their power also creates new challenges: Cities have struggled to build enough housing, pollution abounds, and diseases can spread more quickly. Cities must also manage the massive amounts of traffic — automobile, train, bike, and pedestrian — that can clash and result in deadly accidents.

The world’s cities are constantly experimenting and generating new ideas about how to solve those problems. The difficulty for policymakers has long been: How do we get good ideas to spread? Municipal leaders sometimes labor under the mistaken belief that they have nothing to learn from their peers a few miles away or across the globe. How can we encourage more cross-pollination?

Billionaire Michael Bloomberg, former mayor of New York City, has launched a $50 million global idea-sharing project to facilitate the migration of effective urban policies to allow cities around the world to address their biggest issues.

It’s called the Bloomberg Cities Idea Exchange, a curated marketplace of policy ideas for municipal leaders with hands-on support to help cities implement them. On Tuesday, the project announced the first set of policies that would be added to the exchange, selected by its staff based on assessments of their effectiveness, their cost and complexity, and the perceived interest among city leaders.

While ideas exchanges are not a new concept among policymakers, they risk functioning as little more than passive warehouses, where ideas are placed on a shelf and may never be picked up again if they cannot be easily adapted to a new setting.

The Bloomberg group believes that by including only proven interventions and providing technical support for implementation, their policy-sharing network can thrive. The new exchange will provide grants to support implementation, offer how-to guides from the officials who have already put these policies into place and technical advice from Bloomberg staff, and pay for city leaders to visit other jurisdictions and see the policies in action.

The idea is “to take all of the lessons that have been learned from many experiments all over the globe,” said James Anderson, head of government innovation at Bloomberg Philanthropies. “To create an infrastructure that frankly does not exist in the world that takes good ideas, but marries them with the critical supports necessary to get them into the hands of people who want them when they want them and to help them stand them up so that they survive.”

Urban development has long been one of Bloomberg’s top philanthropic priorities, the target of hundreds of millions of dollars in giving since 2011. He has supported a city leadership program at Harvard and various initiatives focused on US mayors, US cities, and cities around the world. He has paid particular attention to efforts to better adapt cities to climate change and to support public art projects.

It’s a natural fit for the former New York mayor, who has a deep interest and expertise in the challenges cities face. While in office, he traveled to Paris and decided to test out a bike share in New York like the one he saw there; he turned to Bogotá for inspiration on bus rapid transit, jumpstarting a new era of public transit improvements that continued beyond his term.

Bloomberg Philanthropies is stocking the ideas exchange with 11 policy interventions to start, covering the breadth of issues that city leaders contend with, from transportation to air quality to public corruption to infectious diseases:

Some of these ideas aren’t particularly novel — NYC’s first smoking ban was instituted while Bloomberg was mayor in 2003 — but the policies themselves aren’t really the selling point of the exchange.

Instead, the potential value is the knowledge that city officials have accumulated in trying to implement policy solutions and the ability to share those experiences with others who want to try them out. That is where the need truly lies, Yonah Freemark, principal research associate at the Metropolitan Housing and Communities Policy Center at the Urban Institute, told me. He described attending a meeting that brought together leaders from seven neighboring jurisdictions in Minnesota; before that day, the officials said, they had never met collectively before.

“My experience is that every city and the staff who work for that city think that their city is the most unique place in the world,” Freemark said. “That there is nothing they can fundamentally learn from other cities because their specific problems are problems unto themselves.”

The Bloomberg project hopes to break down those silos. Freemark gave the example of low-cost air quality sensors in schools and other areas frequented by children. That policy has already been implemented in Lima, Peru, and has shown a 45-percent improvement in air quality, providing the empirical foundation for its inclusion in Bloomberg’s exchange.

But the real opportunity, Freemark said, would be officials from Lima sharing with their peers in other countries how they found the manufacturer of the low-cost sensors, giving other cities the actionable information that officials are often looking for when they want to adapt policies to their own communities.

“People in other cities may care about air pollution, but they don’t know who to contact about that. They don’t know who [Lima] got in touch with,” he said. “That person in Lima is going to tell them who their contact was at Microsoft or whatever company gave them the air sensor and is going to help to make that connection. That would never happen without this kind of direct communication.”

Josh Humphries, Atlanta Mayor Andre Dickens’s top housing adviser, who has consulted with multiple cities on building homes for the unhoused, told me that the package offered by the Bloomberg exchange “probably solves 80 to 90 percent of the questions that we might get talking one-on-one with 25 different cities.”

The Bloomberg team has tried to anticipate the problems that could hamper such a project, studying the science of implementation and idea replication “to learn about why ideas do and don’t spread,” Anderson said. Every city must navigate its own administrative labyrinth of funding, procurement, rulemaking, and public comment, creating friction for getting any new idea off the ground.

Many ideas clearinghouses, Anderson said, are primarily focused on supplying the policy ideas. The Bloomberg project is equally focused on the demand side, on generating interest in policy ideas among the people who would actually implement them and then providing support for their efforts.

The cities of the future face daunting challenges, from the planetary (climate change) to the painfully human (political polarization and corruption). We won’t know whether the Bloomberg exchange was a well-intentioned flop or a catalyst for real change until its own evaluation comes in — and that could be many years into the future, given the slow pace of urban policy.

“We want to make sure every city that wants one of these ideas and wants to use it well, that we can support them and give them the dedicated resources and support that we think is so fundamental to successful idea replication,” Anderson told me. “We are going to be watching closely and figuring out how we meet the demand that exists.”