As defined in Newman's book "Design Guidelines for Creating Defensible Space", defensible space is "a residential environment whose physical characteristics—building layout and site plan—function to allow inhabitants themselves to become key agents in ensuring their security." He goes on to explain that a housing development is only defensible if residents intend to adopt this role, which is defined by good design: "Defensible space therefore is a sociophysical phenomenon," says Newman. Both society and physical elements are parts of a successful defensible space.