This trend with corners

[Skamp]

If all of the ball has to cross the line to be a goal or out of play, how come only a millimetre of the ball has to be in the quadrant for a corner?

[M42Owl]

Because even a mm on the flag side (including on the line) determines that the ball hasn’t crossed the line, I.e. it’s still in the quadrant.

[Skamp]

I get that but the point I'm making is that all of the ball should be inside the quadrant to be consistent with, say, a goal.

[M42Owl]

Ok, look at it this way…

Does the ball have to be completely within / on the line to be in the quadrant?

or

Does the ball have to be completely outside the line to be out of the quadrant?

Either could be used as the rule, but the law makers decided the first option.

Its a case of, the ball hasn't crossed the line out of the quadrant, so it’s still in it. Hence consistent with the goal line rule.

[Tylluan]

The line is part of the area of play, or playing surface. The ball doesn't go out for a throw in/corner/goal kick until it's over the line. Similarly a goal isn't scored until the ball is over the line. Therefore the ball isn't out of the corner until it's fully crossed over. 

In field hockey the goals are set off the back line, not on it like football, to give an unobstructed view of whether the ball has actually crossed or not.