from Somewhere in the Night by Nicholas Christopher:
The city as labyrinth is key to entering the psychological and aesthetic framework of the film noir. As the German historian Oswald Spengler wrote in The Decline of the West, speaking of the megalopolis or “world-city” of the twentieth century: “The city is a world, is the world.” He went on to characterize twentieth-century man as one who “is seized and possessed by his own creation, the City, and is made into its creation, its executive organ, and finally its victim.” The city as a closed system. A beast with a life of its own, into whose guts the hero’s quest is undertaken.
The city is a labyrinth of human construction, as intricate in its steel, glass, and stone as the millions of webs of human relationships suspended within its confines. It is a projection of the human imagination, and also a reflection of its inhabitants’ inner lives; and this is a constant theme — really, a premise — of the film noir. In these films, the framing of the city, our visual progression through the labyrinth, is as significant an element as plot or characterization. The oblique lighting and camera-angling referred to, in both studio and location scenes (especially the night-for-night shoots), reinforce our implicit understanding that the characters’ motives are furtive, ambiguous, and psychologically charged; that their innermost conflicts and desires are rooted in urban claustrophobia and stasis; and that they tread a shadowy borderline between repressed violence and out-right vulnerability. Hence the obsessive emphasis on urban settings that are precarious and dangerous: rooftops, walkways on bridges, railroad tracks, high windows, ledges, towering public monuments (a Hitchcock favorite), unlit alleys, and industrial zones, not to mention moving trains and cars.