"Privately Owned Public Spaces (POPS) are open to the public, and include plazas, arcades, atriums, hillclimbs, and green streets. These spaces are allowed or required by rules in the Seattle Land Use Code that have been in place for several decades, and are generally located in Seattle's Center City. Other POPS may be open to the public as a result of a street vacation (permanent closure of a street). These spaces can be located in neighborhoods throughout Seattle, wherever a public space is created as a public benefit ."
This process requires oversight and proper planning since its ultimate goal is to apease both developer and everyday user. "In New York, planning officials in the late 1950s began offering private developers additional height and density in exchange for light and public open space. This “incentive zoning” generated hundreds of plazas, arcades, walkways and pocket parks owned and maintained by property managers. New York journalist Adee Braun has described the Big Apple’s POPS as “urban nesting dolls [that] were built to provide the public with shortcuts, shelter and gathering spaces.”
More info here from a past blog post:
http://civilizedurbanplanning.blogspot.ca/2016/05/privatization-of-urban-planning.html