Oh, I think I finally got it.
The term "depth" was confusing me, making me think of a vertical measure while it's actually a horizontal measure. Although I will not need it, I try to get it right for the sake of curiosity.
To say it the easy way, "width" is the distance from shoulder to shoulder, "depth" is the distance from chest to back and "height" is the distance from head to feet, all of them calculated for a human who has the eyes at a height of Z. So only width and depth are used on 2D plan view, while height will only be useful in the 3D view.
I'm right this time? At least I hope to be closer to the answer...
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If a long walk every day were healthy, mailmen would be immortal.
