I know Z as upward. X and Y were always on the base plane representing length and width. Z comes in being all like, “Now we’re being 3D!”
So wherever the “floor” is, represented with gridlines, boundary, canvas, etc. that’s where they live. That is Flatland where there is no up or down. It is 2D where most of my work is. If you try tell me Y is Z, I’d ask “wtf is a Z?”














You’re mixing up perspective with the object’s actual coordinates system. The “left-right-up-down” are your perspective or computer screen and do not define the axes of the object itself. The object has its own.
If I rotate a map on a table, it’s X and Y don’t suddenly flip. The coordinates belong to the object, I’m just viewing them from a different perspective now.
In mathematics, the Z axis only exists because it’s defined as being perpendicular to an existing plane (the plane X and Y form). The gridlines represent that plane and Z’s extrusion values reference it. Your perspective or viewing angle don’t influence these coordinates at all.
Commonly we face the XY plane down as it’s “floor”. We build things from the ground up. We draw from top down. It’s just how gravity brought the standard around. You can flip it however you want, though. But if you see a grid, that’s a plane and Z is extrusion off that.