Shaving the hair below the navel

We have to shave the hair below the navel. Now what I want to know is that do we shave from immediately below the navel, which is the stomach area? So in other words do we have to shave our stomach?
And if so, do we shave the complete stomach from 1 side to the other? Or do we shave from the area just below where the underpants normally start? I always thought that we had to shave from just below where the underpants normally start downwards. Please explain?