Think about the green and leafy places that make your town such a great place to raise a family. Maybe it’s the trail along the lake where you taught your kiddo to ride a bike. The community garden where he grew his first tomato. Or the neighborhood dog park where the whole brood goes to burn off some energy.

No matter where you live, you’ve probably clocked countless hours at the playground. My two-year-old and I spend so much time at our corner park, I feel like the mayor. Where else can I take a shrieking toddler who has awoken ready to party at an hour before most of the adult world has finished its first cup of coffee? Where else can he hurl himself down the twisty slide 27 times while I swap tips—or just commiserate—with my fellow tired parents? If we didn’t have a park within easy-toddling distance, I think we’d both go nuts.

Fortunately for the mental health of my whole family, we live in the San Francisco Bay Area, home to the third best city park system in the country. An amazing 98% of San Francisco residents live within a 10-minute walk of a park, according to ParkScore ®, the index that measures how well the 50 largest U.S. cities are meeting the need for parks. (Find out how your city stacks up at Parkscore.tpl.org).

In my day job, I’m editor at The Trust for Public Land, the nonprofit that crunches the data behind ParkScore. Before working here, I didn’t think much about what it takes to sustain the parks and trails that make the Bay Area such a gorgeous place to live. Like the hills, or the fog, our parks are such an integral part of daily life, they feel like a given.

But in reality, great parks are not just some force of nature, beyond the control of everyday people like you and me. They result from the efforts of a community that recognizes the benefits of parks and natural spaces—and fights to prioritize them. And as ParkScore illustrates, too many cities are still struggling to manage this balancing act.

Their success will have real world repercussions for families everywhere. Research shows what we’ve all experienced: parks make cities happier and healthier. Kids who live within walking distance of a park are more likely to maintain a healthy body weight and higher levels of physical fitness. A simple 20 minute walk in the park can be more effective than medication to manage a child’s ADHD. In this age of increasing rates of obesity and other diseases related to inactivity, parks may be one of the defining factors shaping public health nationwide.

So what can you do to stand up for your local parks?

• As ParkScore shows, big cities average 2.4 playgrounds for every 10,000 residents. Does yours? Find out on this list or by calling your local parks department. If your city falls short, ask City Hall to construct more parks—for the health and wellbeing of the whole neighborhood.

• Join (or start) a local “Friends of” organization. Local citizen activism is crucial to maintaining attractive, safe parks.

• The simplest way to support your local parks is to spend time in them. Your kids will have fun and make new friends—and you will too. Maybe the mom standing by the swings sipping her travel mug of coffee has great advice for getting your early-riser to chill out in the mornings. Or if not, at least she’s a friendly face who understands exactly how much this park means to you.