Bu Jian Tian (Translates to not seeing the sky) refers to the cut of the pork from the armpit which has a very high fat to meat ratio. There are also some leaner parts. The portion will be a mix of the fatty bites and leaner parts.
Pork Belly would have a firmer bite, but still a very good ration of meat to fat. If you prefer a firmer meat bite, pork belly is your choice.