Typically, the origin and at least some of the coordinate axes of each space are different, providing different perspectives to the designer.
It may not be possible to discern from an illustration to which space a point, ray, or plane belongs unless some convention is adopted.
The only exception is the use of F and F′ to indicate respectively object and image space focal points (which are not conjugate).
One may wonder how an object point can exist on the "output" side of an optical system or conversely how an image point could be located on the "input" side of an optical system.
It is common practice to designate the horizontal axis of an optical space as the z-axis with the positive direction left to right.