German photographer Thomas Birke is fascinated by metropolitan areas. Here, he shows us a side to Hong Kong we don't often get to see. "I am most interested in density," he says. "My aspiration is to show at least 1,000 people or their traces on every picture. Be it the illuminated windows of their apartments, the light streaks of their vehicles or their clothes hung out of windows for drying. Even if you do not see people directly, you can see their footprint on the urban environment."