On the endogenous dimension, postal density could in principle be tuned by the postal operator by adjusting quality of service.
Postal density would change if the postal operator changed the quality of service.
Nothing that the postal operator can do will affect the postal density.
A female holds up an utensil.
Trombonist playing for a football game.
Two people are in a garden.
It consists of a freeze frame.
A man digs a ditch.
I was never a big fan of him, despite his playing.