There is already the Big Book of Breasts, Butts, and Püssy. What does he hope to add to the genre? And why is everything a "project" these days?
Once a civil servant, Heng has become a renowned artist and is a pioneer of contemporary art in Singapore.
The project aims to defy the "demure" image of a Singapore Airlines stewardess, who is seen as an icon in Singapore and a "standard for feminine identity".
In a 2013 interview, Heng said that she realised people, including herself, have never seen how their bottoms look like even though it's an important part of the body, just like the face.
What provokes thoughts is not just the photos of the bare bottoms but also why people participate in this project, Heng added.
"Women (who) participated become more aware or begin to raise questions more about their own role as a woman and their position in the society... and also issues of representation," Heng explained.