“Lungs for the Metropolis”
Olmsted was part of a movement that saw the urban park as essential to urban life -- a green oasis with fresh air and open spaces. He was a social reformer who believed that parks could be unifying places where people from all classes of society could mingle and experience nature as a sanctuary, enjoying its tranquility and beauty.
As the population of New York City grew rapidly between 1820 and 1880, there was a strong push to develop more park areas for city dwellers.
The New York Park Association noted in its 1882 treatise, “More Public Parks!:”
“The time has arrived when the public mind should be thoroughly aroused to the imperative necessity of providing for the present and future wants of our rapidly increasing population, in the important matter of park area. . . . the urgent need for more and larger breathing places.”
They viewed city parks as "Lungs for the Metropolis:"
“Imagine such a park with tens of thousands of our population enjoying themselves according to their different tastes and inclinations, drinking in the pure and invigorating air, or taking part in healthful and bracing physical exercise.”
In addition to the values of recreation and health, there was also a moral and aesthetic component to the proposals for more urban parks:
“It may not be out of place to refer to another advantage to be derived from parks. . .outside of the social, sanitary, and financial advantages: the effect they will have on the manners and habits of the people, their potency in developing the finer feelings, the moral faculties, the artistic instincts, and the latent genius that may be slumbering among our growing population.” 
 New York Park Association. More Public Parks! : How New York Compares with Other Cities : Lungs for the Metropolis : The Financial and Sanitary Aspects of the Question. New York: The Association, 1882. p.5.
 Ibid. p. 9
 Ibid. p. 9