Roads, Rooms and Rails

One-point perspective is not only for boxes. Roads, railroad tracks, hallways, rows of trees and the inside of a room seen straight on all use it. You already know the rule from One-Point Perspective: lines that go straight back meet at the vanishing point.

A road, its center dashes and a row of posts, all going back to one point.

There is a second idea here that surprises people. Fence posts that are equally spaced on the ground do not look equally spaced in a drawing. The gaps shrink as they go back, and the posts get shorter.

Key idea

Lines that go straight back meet at one vanishing point, and equal spaces on the ground look shorter and shorter as they go back.

Why it works

How big something looks depends on how far away it is. A post twice as far away looks about half as tall. The same is true of the gaps between posts: the far gaps are farther from you, so they look smaller. That is why railroad ties seem to crowd together near the horizon.

Worked example: Fence posts

A fence post 10 meters away is drawn 6 cm tall. An identical post stands 20 meters away. About how tall should you draw it?

Its distance doubled, from 10 m to 20 m.
Drawn size goes down in step with distance: twice as far looks about half as big.
Half of 6 cm is 3 cm.

Answer: About 3 cm.

Worked example: A room

You stand in a doorway and look straight into a room. Where do the lines where the walls meet the floor and ceiling go?

Those lines go straight away from you.
In one-point perspective, lines going straight back meet at the vanishing point.
The vanishing point is on the horizon line, at your eye level on the far wall.

Answer: To one vanishing point at your eye level on the far wall.

Common mistake

People space railroad ties or fence posts evenly on the paper. That makes the road look like it tilts up like a wall. Let each gap be a little smaller than the one in front of it, and let the posts shrink as they go back.

Canaletto painted views of Venice in careful perspective. In this one, the long rows of arches along the square lead your eye back to the far end.

The Square of Saint Mark's, Venice, by Canaletto.

The geometry behind "twice as far looks half as big" is in the Math Ladder's Similar Figures.

Roads, Rooms and Rails

Practice

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Sources and further reading