Urban-Planning or zoning is done an area is designated for parks or other recreational uses. Considered to be open to the public these green spaces are sometimes privately owned. Publicly or privately owned these green open spaces often contain the same characteristic. Waterfeatures, Large grass fields, or a highly maintained natural landscape for wildlife. 

Bushnell Park, Hartford, CT - Hartford, Connecticut - Downtown Park  Provides Setting for Activities and Boasts Only Municipal Park Art Gallery  in All of State

Even though these areas are designated for recreational uses the reality is the city is hovering over the occupants awaiting with all the hazards of polluted air, higher temperatures, and more.

Green spaces do have tremendous benefits. They offer a large area to encourage exercise, Socal events, lower the pollution in the area, and decrease noise pollution. They also help lower the temperature of the area caused by the heat island effect.

Examples of green spaces;
-Parks (partly or completely covered with greenery)
-College campus communal area
-Wildlife protected area
-Green roofs