Circles in a Vertical Plane.
The planes of the circles at the end of a cylinder lying on its side are vertical in reality.
To draw a cylinder lying on its side, draw a line representing the axis of the cylinder.  If the length of the cylinder is not going away from you - i.e. it's going across you field of view- then draw the axis parallel to the horizon.  The major axis representing the circles on its ends will be perpendicular to the horizon and the elipses will be very thin.
If, however, the cylinder is lying so that its length is receding (below) then draw the cylinder's axis to a vanishing point that represents the direction in which the walls of the cylinder are receding.

  Next draw the major axes of elipses that will represent the circles at the ends of the cylinders. Draw these axes perpendicular (90 degrees) on your paper to the cylinder axis.   The major axis of the elipse of the more distant circle will be shorter due to the convergence of the cylinder walls on the vanishing point. The minor axes of both elipses is congruent (define) on your paper to the cylinder's axis.
Which elipse is fatter?
Why?

Do this:
   Draw four cans lying on their sides in different directions scattered various distances from you on your table near eye level.
 
 
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