The character of an urban void is defined by the built surrounding. It determines the appearance and the function of the enclosed space. This particular approach to model urban form distinguishes three major zones of this urban phenomenon: 1. Core, 2. Transition Zone, 3. Surrounding. The transition zone contains the capacity to determine the prospective character of the framed void. It offers the possibility to intervene in the existing urban form not by filling but by emptying it. The void experiences a transformation from a neglected urban object to a clearly identified urban subject. This threshold towards the void serves as a mediating element between the two coexisting situations. It acts as a "coulisse" of an urban theater towards the void.