San Francisco and Sacramento have the best citywide parks systems, according to a brand new ranking of the 40 largest American cities by the Trust for Public Land. Both cities received a score of 4.5 out of 5 on “Park Benches.” Fresno, California, was the lowest ranked of the top 40 cities, with a score of just 0.5.

Other cities ranking highly include Boston, New York, Washington, D.C., and Portland, Oregon.

The rating system, ParkScore, is based on more than a year’s worth of data from cities and parks departments around the country. The scores are a composite of five factors: median park size, acreage as a percent of city area, percent of residents living within a 10-minute walk of a park, park system spending per resident, and the number of playgrounds per 10,000 residents.

“Even if you have a big city or a small city, a dense city or a more spread out city, an older city or a younger city, we feel that those factors all point to a pretty fair way of judging cities against each other,” says Peter Harnik, director of the Trust for Public Land’s Center for City Park Excellence. He says advanced GIS data enabled a more detailed analysis of spatial information, including pedestrian barriers like train tracks or paths uncrossable without a bridge.

In addition to the rankings, the Trust for Public Land has created a website where the complete data from all the rankings can be seen. Users can also see block-level maps showing the most park-accessible areas in these cities.

No one city performed ideally across all these metrics. Top ranking San Francisco, for example, has a median park size of just 2 acres, while 8th-ranked San Diego has a median size of 6.7 acres. And while Virginia Beach has the highest number of parks per 10,000 residents in this list – 5 – the city ranks 7th.

Harnik notes that a wide variety of factors determine how well a city’s parks serve its people. The number of playgrounds may be the most important.

“We feel a playground is really a basic bottom-line measure of what a city park system is doing for its residents. Obviously playgrounds are great for children, but they go way beyond children. They’re community gathering areas, they are so important to the social network of a neighborhood and a city,” Harnik says. “It’s somewhat of a predictor of the other kinds of facilities that a city parks department provides its citizens.”

Those at the bottom of the list – cities like Fresno, Charlotte, Louisville, and Mesa, Arizona – perform fairly low across all five factors. Harnik says this underscores some of the historical and social conditions that limit cities’ ability to provide parks. Density, poverty, car ownership and physical layout all play a role in determining the value and need of parks in cities. Those cities built before the car began to influence city design, like Boston or New York, have an urban form that makes parks more accessible than those cities built largely after the car, such as Tucson or Houston. And for cities like Fresno, where backyards are commonplace, the need for parks may seem lower.

“Even though a backyard is by no means as good as a park, it does fill in some of the services that parks bring,” Harnik says. “But we’re never going to be able to replicate the full panoply of parks experiences and opportunities on a privatized level.”

This is especially true in less affluent neighborhoods and cities, according to Harnik.

“Cities that are denser and poorer get more benefit from their parks and deserve and vote for better parks systems,” he says. “Other places, it’s a harder thing to get public support for.”

Harnik hopes the rankings will help show cities ways their parks systems can improve, and that the data will help residents to take more action to get parks where their needed. No city on the list received a perfect score. As Harnik argues, there’s always room for improvement.

Go to http://www.theatlanticcities.com/neighborhoods/2012/05/best-city-parks-systems-america/2052/ to see the entire list and links..