Produced in part by the fine folks at SPUR (San Francisco Planning & Urban Research Association), this map indicates POPOS (Privately Owned Public Open Spaces). Many of them, it seems, are not visited nearly enough.
Scattered across the centre of San Francisco are almost seventy semi-secret spaces, privately owned but open to the public. Subject to the fine print of a little-known pact between City and Commerce, these so-called POPOS (Privately Owned Public Open Spaces) allow alluring vistas of San Francisco and access to its intimate interiors. However, they are often poorly indicated - perhaps a deliberate tactic by the private companies who own the spaces to prevent the pesky public from using them. Accessing POPOS sometimes even requires walking past security guards, or through unmarked doors. No wonder many are under-frequented.
The round indicators are spaces set up between 1959 and 1985, the squares denote the 23 "inaugurated after the 1985 Downtown Plan, which stipulated the zoning regulations requiring commercial urban development to be counterbalanced by POPOS."
Comprehensive information about POPOS history and regulations can be found here. Strange Maps also details each park for your convenience. Read more about said POPOS after the jump.