The Aboretum as a public, private space.

I am interested in the ways that people take the Arboretum, a very public, open space, and make their own private areas within it with little physical adaptation of their environment. People frequently engage in activities that denote some expectation of privacy or intimacy within the space with little demonstrated or appreciable hesitation that would result from being publicly exposed. So I want to know why people feel as though they can make a public space a private one, and how they do that satisfactorily.