Minecraft - Where are doors technically located?

"The center of a village is the centroid / average of all the doors coordinates"
(https://minecraft.gamepedia.com/Tutorials/Village_mechanics#Terminology)

What I'm wondering is which point is this referring to? The block below the door, the lower half of the door, or the upper half of the door?

Minecraft launcher blocked at School?

I don't have administrative password and Minecraft won't open because the launcher is blocked. I've tried every trick and Minecraft won't work because the launcher is blocked, not the app itself. How do I fix this?

Added (1). its not working at home. It just won't let me open it.

Upgrading my Graphics Card. Do you know any good gaming ones?

I currently have a GeForce GT 720 which is absolutely terrible, can hardly handle Minecraft xD

I was just wondering if you guys have any suggestions for a card that can handle gaming with high graphics settings (preferably not too expensive)