Public spaces are not only spacial or geographic, but extend wherever law might extend. A class of behavior becomes public space, I believe, when it is regulated by legislation. Control over employment practices, when legislated, becomes public space, a space in which the power of ostracism can no longer act effectively. An example is the public roads. Government overrides private property rights, piecemeal, through regulations which take from private parties the choices which formerly characterized private ownership.
Examples are laws regarding employment practices and building codes.
Decisions constrained by government, such as the placement and number of electrical outlets in private residences, become public space. Private property rights are uneconomic, too expensive to establish and maintain. This is true, for example, in frontiers not yet populated. Now I am not saying that public spaces go completely without control. Policing does happen in public spaces.