Golden Gate Park is 2.1 times larger than Prospect Park (Brooklyn).
Area: 4 km2 calculated
Golden Gate Park, located in San Francisco, California, United States, is a large urban park consisting of 1,017 acres of public grounds. Configured as a rectangle, it is similar in shape but 20 percent larger than Central Park in New York, to which it is often compared. Wikipedia
Area: 2 km2 calculated
Prospect Park is a 585 acres public park in the New York City borough of Brooklyn located between Park Slope, Prospect-Lefferts Gardens, Ditmas Park, Windsor Terrace and Flatbush Avenue, Grand Army Plaza and the Brooklyn Botanic Garden. Wikipedia