In a one-point perspective drawing, imaginary vanishing lines along an object recede to one vanishing point on an imaginary horizon line (in this case, think “eye-level line”) in the distance.
Accordingly, the object diminishes in size as it gets closer to the vanishing point.
▼ Sample one-point perspective drawings–classic examples include a road or railroad tracks stretching into the distance.
Even though it was supposed to be a one-point perspective drawing there were actually two vanishing points.
When I tried to turn them into one vanishing point the image always changed in some way.