Sorry, got nerd sniped: Isn't it usually the y coordinate that stands for the vertical axis? At least that's how I know 3D coordinate systems, with the z axis either increasing towards or away from the center, left handed vs right handed coordinate systems.
In GIS parlance, elevation is typically z coordinate. Which of x and y correspond to east-west and north-south varies from coordinate system to coordinate system, and is a bountiful source of stupid bugs (at least for me). But yeah, in 3D graphics z is usually distance from the camera I think.
I see, fascinatingly inconsistent :D I somehow have the urge to popularise a coordinate system where the x axis represents elevation now.
Towards or away from the center is the height, no? As in, you’re the bird at height Z observing the x-y plane under you, and the Z axis goes into you. Or away from you if you happen to be a mole under ground.