On a third, holistic option, causality runs in both directions. Two examples of such are (a) systems analyses, which take built structures as social systems that contribute to social function, and (b) urban sociology, which takes the city en gros as social structuring of space which shapes its habitants, who in turn shape the city (Simmel 1903). As expanded to environmental sociology, the suggestion is that built environments promote patterns of living, working, shopping, and otherwise conducting commerce among groups and in relation to other individuals.