For years, public health experts have urged people to spend more time outdoors for the nourishment of their minds, bodies and souls.

Those recommendations have taken on a new urgency this year as the nation grapples with a pandemic that seems to be especially virulent in crowded indoor spaces. The Centers for Disease Control and Prevention now lists visiting parks and recreational facilities — particularly those “parks that are close to your home” — as a way to protect yourself and others from covid-19.

But for tens of millions of Americans, that’s easier said than done; according to the Trust for Public Land (TPL), a nonprofit group that works to protect parks and other outdoor public spaces, roughly 100 million Americans don’t have a public park within a 10-minute walk of their home.

“For far too many communities, quality green space where families can recreate and practice social distancing is simply not available,” said Diane Regas, the president and chief executive of TPL.

TPL maintains a national database of park infrastructure in 14,000 cities and towns. On average, about 55 percent of Americans have easy access to a local park, or one that is within a 10-minute walk from home. In the top-ranking cities, such as Minneapolis and Washington, D.C., 98 percent of residents have easy access to a park.

In the least accessible cities, such as Charlotte and Indianapolis, fewer than 40 percent of residents live within 10 minutes of a park. Research has shown that such disparities in park access can be linked to obesity, and affect longevity and mental health.

The CDC’s National Environmental Public Health Tracking Network maintains a separate measure of park access, showing a nationwide patchwork of accessibility. In 2010, for instance, roughly 39 percent of Americans lived within a half-mile of a public park, with a state-level variation ranging from 9 percent in West Virginia to 88 percent in Hawaii.

Other researchers have explored various neighborhood factors associated with park access. Using the CDC data, for instance, Brookings Institution researchers found that, at the metropolitan-area level, “regions with lower park access tend to have higher poverty rates.”

Studies also have shown that areas that are whiter, richer and more highly educated also have better access to urban green spaces.

TPL researchers are finding that even when park access is available, the quality of parks is highly correlated with neighborhood demographics.

“On average, parks that serve a majority of people of color are half as big (45 acres compared with 87 acres) and serve nearly five times as many people per acre (24,000 compared with 5,000), compared to parks that serve a majority white population,” said Linda Hwang, TPL’s director of strategy and innovation. That higher density makes it more difficult to maintain social distance in parks that serve majority nonwhite populations.

“When we look at park size and park crowding, parks that serve low-income communities and communities of color are often smaller and serve more people,” Hwang said. “This increases park pressure, which is particularly relevant during the pandemic and a time of social-distancing.”

The pandemic has placed the nation’s parks in an odd bind: Traffic to local parks is up dramatically as people seek safe outdoor places for recreation. Online searches for terms like “trails near me” and “state parks” have spiked to unprecedented levels in recent months.

But money to staff and maintain those parks is drying up as states and cities face severe budget shortfalls due to the ongoing recession. And that’s happening on the heels of steep park cuts imposed as a result of the previous recession.

In the coming year, parks and recreational facilities will be just one of many municipal spending items on the potential chopping block as municipalities and states look to plug the holes in their budgets. A study conducted by the National Recreation and Park Association, a nonprofit group, found that local officials tend to view park funding as “being fully discretionary and as a luxury.”

Far from it. TPL’s Regas says the pandemic underscores how parks are “an essential part of our public health infrastructure.” And the uneven access to that infrastructure across the nation is, in turn, a public health problem.