MICHAEL WOLF LIVES and works in Hong Kong, one of the world's most densely populated urban centers. As many as 6,700 people occupy each square kilometer of the city, most living in high-rise apartment buildings. In "Architecture of Density" at the Robert Koch Gallery, Wolf explores this population density through the architecture of the city. He takes pictures of skyscrapers from the windows of other skyscrapers, often without reference to the sky or ground. The results entail formal abstractions of line and color. Rows of windows produce diverse patterns, which instill a sense of syncopation and movement despite the fixity of these enormous structures and Wolf's almost flat focus. Colors pop out across the buildings' facades in long columns and variegated motifs, occasionally interrupted by construction, which one surmises, must be always underway. But the abstraction in Wolf's photographs isn't merely formal. Through his study of Hong Kong's architecture, he presents modern social life as materially overdetermined. The picture frame is often completely filled, and you gets the impression you could move about the city from building to building without ever touching the ground. Concrete and steel are ubiquitous and appear to structure any possible action or interaction. Wolf's cityscapes betray evidence of human life but show no sign of willful activity. People appear as remote figures in the sea of cubicle apartments across the way. They belong to the material density of the city and contribute to the sense of claustrophobia it induces, but they don't provide companionship or shape their world as self-determining subjects. In the exhibit Wolf explores the material conditions of the modern mass subject, situated and defined by forces beyond his or her control. His photographs are successful insofar as he doesn't dissociate his point of view from these conditions but rather suffers them through it. Architecture of Density #18 shows multiple stories of a gigantic, block-wide building surrounded by the gray canvas of scaffolding, like a nightmarish variation on Christo's playful wraps. Wolf's camera is immersed within the city he depicts, and his photographs bear the psychological weight of its density. Reception Fri/4, 5:30-7:30 p.m. Gallery hours Tues.-Sat., 10:30 a.m.-5:30 p.m., 49 Geary, fifth fl., S.F. (415) 421-0122. (Clark Buckner)