In the last couple of years, at least 72 more parklets have materialized worldwide in places like Philadelphia, New Orleans, Seattle, Chicago, Mexico City and Auckland, New Zealand. (In cities with cold weather, sponsors of parklets are typically required to remove them in winter.) This year, the Los Angeles metro area will welcome four of them, sponsored by local business improvement districts and chambers of commerce. In San Francisco, parklets are open to the public, but they’re typically commissioned by small businesses hoping to attract customers, brighten streetscapes and create gathering spaces.

It usually takes 12 to 18 months for a business to get a permit and build a parklet; the cost can range from roughly $8,000 to $14,000 a parking spot, according to Mr. Ocubillo. A majority of parklets are privately financed and maintained. But in San Francisco, some have received partial funding from the city.

The idea for parklets began to germinate in 2005, when members of a San Francisco arts collective called Rebar wanted to apply their artistic flair to small fragments of real estate. They were also interested in challenging “the boundaries of the short-term lease offered by a metered parking space,” says John Bela, one of Rebar’s co-founders. And they questioned what they saw as an automobile-centered approach to urban planning and design.

They started an experiment. In a stretch of downtown San Francisco that lacked greenery, they found an empty parking space, rolled out a patch of grass turf and set up a park bench and a potted tree. They put up a sign that read, “If you’d like to enjoy this little park, please put some coins in the meter.” Then they went across the street to watch.

The land next to a parking spot, Mr. Bela says, probably rented for a couple of hundred dollars a square foot per year, “but you could rent this little piece of land, 200 square feet, in downtown San Francisco for a couple dollars an hour.”