What is physical structure?

Physical structure is the way space is arranged. In homes and buildings it is about the size and the arrangement of all spaces such as rooms, hallways, corridors, stairs, floors, ceilings and so on. This arrangement includes the immediate surroundings of buildings such as gardens and playgrounds.

Architects formulate plans in which the functional relationships between different spaces are defined and elaborated into the actual design. In the context of this website measures which have to do with physical structure are mainly subsumed under ‘design’.
More about this here.