If you've ever been to Hong Kong, you'll know that its one of the densest places anyone's ever lived in and ever built. It's population of 7.07 million live in the sky.
Michael Wolf created "Architecture of Density" to point attention to Hong Kong's housing problems. There are 6,588 high rise buildings, and its becoming even more packed than New York's 5,818 buildings. There are more buildings per square kilometer and they're much taller than anywhere else.
The reason for this is because only 23.7 percent of Hong Kong's land can be developed. So hence, the reason to build everything vertically. Check out the gallery below for Wolf's work: