What is the horizon line in perspective drawing?

The viewer's eye level carried across the picture as a line. All horizontal vanishing points sit on it, everything above it is seen from below and everything below it from above, and it exists in every picture, including a windowless room, whether or not a real horizon is visible.

Is the horizon line always at eye level?

Yes, by definition. Sitting lowers it, standing raises it, a ladder raises it further. Choosing where to place it in a drawing is choosing where the viewer stands.

Where should the horizon line go in a drawing of a room?

At a standing eye, about 160 centimetres above a floor in a room about 250 high: roughly two thirds of the way down the far wall from the ceiling, a little below the middle of the picture. Higher than that and the viewer is floating.

How do I find the horizon line in a photograph?

Extend two receding edges of one wall until they cross; that crossing is a vanishing point and the horizon passes through it. Or find two standing people of the same height on the camera's ground: if the camera was at eye height, the line through their eyes is the horizon.

Why is there no horizon in my photograph of a tall building?

Because the camera was tilted up. The horizon is still at eye level, but the tilt slides it down the frame and out through the bottom edge. The two horizontal vanishing points are on it, below the picture; the third point, above, is not.

Is the horizon line the same as the skyline or the edge of the sea?

No. The skyline is where buildings meet the sky, at any height. The sea's edge coincides with your eye-level horizon only when you stand at the water's edge; from a cliff it lies well below it. Draw the eye level and let the sea fall where it falls.

The Horizon Line Is Your Eye Level: What That Decides in a Drawing

The horizon line in a drawing is your eye level, carried straight across the picture. It is not the edge of the sea or the skyline; it is the height of your eye above the ground, drawn as a line, and it is there in a windowless room as surely as on a beach. Every horizontal vanishing point sits on it. Everything above it you are looking up at, everything below it you are looking down at, and the eyes of every standing person your own height, near or far, fall exactly on it. It is the first line a perspective drawing needs and the one that decides where the viewer is.

One Line, Fixed by Where Your Eye Is

Stand on a flat floor and look level. Every horizontal line that runs away from you, floor boards, table edges, the tops of walls, converges towards a point at the height of your eye. Different families of horizontal lines converge to different points, but all the points are at that one height, so they lie on one line. That line is the horizon. It has nothing to do with whether the actual horizon is visible; the room has one, the cellar has one, a picture of a single table on a floor has one.

Because it is your eye level, it moves when you do. Sit down and it drops to the height of a seated eye, about 120 centimetres; stand and it rises to about 160; climb a ladder and the tabletops that were edge-on open out beneath you. Nothing in the room has moved. The horizon is a fact about the viewer, and choosing where to put it in a drawing is choosing where the viewer stands.

In the construction below the horizon is the level line through the two points. It has no handle of its own, because it is not part of the construction; it is what the construction implies. Drag either point up or down and the horizon rises or falls with it, and the house shows more of its roof or more of its underside. Drag the two points to different heights and the horizon tilts, which means your head is tilted, and every level edge in the picture will disagree with the frame.

Drag a point (Left, Right) and the house follows. Arrow keys move a selected point one step; shift, ten.

Put the horizon below the house and you are lying on the ground looking up at it. Put it above the roof and you are on a hill. Put it through the middle of the walls and you are a person standing in the street, which is what most drawings want and most beginners avoid, because a horizon through the middle feels too plain to be right.

Where It Is in Each View

In one-point and two-point perspective the horizon is a straight line across the picture and every vanishing point sits on it. In a level view it lies where your eye is, which for a standing viewer in a room means a little below the middle of the picture, crossing the far wall about a third of the way up.

In three-point perspective it is still straight and still at eye level, but the tilt of the view moves it in the frame. Looking up pushes it down; looking down pushes it up. Tilt steeply enough and it leaves the picture altogether, which is why a photograph taken up at a tower shows no horizon: it is there, below the bottom edge, with the two side points on it. The third point never sits on the horizon; that is what makes it the third.

In curvilinear perspective the horizon bows like every other line, flattening towards the side points and bulging in the middle. It comes back straight in exactly one case, when it passes through the centre of the frame, because a line through the centre of vision is the one line the projection cannot bend.

Alberti already knew where to put it. His construction of 1435 places the point on which the floor converges at the height of a man standing in the picture, so that the horizon of the painting runs through the eyes of its standing figures. That is the rule in one sentence, and it has not changed.

How to Find It in Any Photograph

The horizon is rarely visible in a photograph of a street or a room, but it is always recoverable, because the picture has already done the geometry. Three checks, in the order they are most useful.

Standing figures. Find two people standing on the same ground as the camera, one near and one far. If the camera was at eye height, a line through both their eyes is the horizon, and it is level. If their eyes are not on one level line, the camera was higher or lower than an eye, and the line through matching points, both waists or both heads, still gives you the direction.
Two receding edges of one family. Extend the top and bottom edges of a wall until they cross. That crossing is a vanishing point, and the horizon passes through it. Do the same for another wall and the line through the two crossings is the horizon itself.
Where the floor turns edge-on. Tabletops below the horizon show their top surfaces; those above it show their undersides. The height at which a horizontal surface would appear as a single line is your eye level.

The perspective grid tool does the second check for you: it finds the straight edges in the picture, finds the point each family agrees on, and draws the horizon through the points it found. The how-to shows how to judge whether the reading is sound.

The Exercise: Three Figures on One Horizon

A sheet of Letter or A4 in landscape, a hard pencil, a ruler, fifteen minutes. No perspective grid is needed for this one; the horizon is the whole lesson.

Rule the horizon 89 millimetres (3.5 inches) from the bottom edge on Letter, 85 on A4. You are a standing viewer.
Draw a standing figure your own height near the left edge, with its feet 60 millimetres below the horizon and its eyes on the horizon, which makes it about 64 millimetres tall, the top of the head 4 millimetres above the line. The eyes must fall on the horizon, because the figure is your height and stands on your ground.
Draw a second figure of the same height twice as far away, near the centre: feet 30 millimetres below the horizon, eyes on it, about 32 millimetres tall. Distance shortens the figure from the feet up and from the head down towards the one line, never away from it.
Draw a child, two thirds of your height, at the same distance as the first figure: feet on the same line as the first figure's feet, about 43 millimetres tall. The child's head ends 17 millimetres below the horizon. A shorter person's eyes are always below your horizon, however near or far.
Now move the viewer. On a second sheet rule the horizon 30 millimetres from the bottom, as if you were sitting on the ground, and redraw the three figures with their feet 20 and 10 millimetres below the line. Every head is now above the horizon and you are looking up at all of them.

The check is a single question about every figure in the drawing: is this person my height, and if so, are its eyes on the line? A drawing in which the eyes of same-height figures wander above and below the horizon has several viewers in it, and it looks it.

The Two Places It Is Put That Ruin a Drawing

Too high. The commonest fault in an interior. A horizon near the top of the picture describes a viewer near the ceiling, so the tabletops open out like plates on a shelf and the room reads as a doll's house seen from above. A standing eye is about 160 centimetres off the floor in a room 250 high: the horizon crosses the far wall about two thirds of the way down from the ceiling.
Tilted. Two vanishing points at different heights make a horizon that is not level, which means a head that is tilted. Every level edge in the picture then runs against the frame. Fix the points to one line before drawing anything else.
Drawn where the sea is. On a beach the sea horizon and the eye-level horizon coincide only when you stand at the water's edge. From a cliff the sea's edge is far below your eye level and the two lines are different. Draw the eye level; the sea falls where it falls.
Moved between objects. A table drawn with its horizon at one height and a chair beside it at another gives the drawing two viewers. One picture, one eye, one line.
Forgotten in a room without a view. A windowless interior has a horizon exactly as a landscape does. If it is not ruled, every receding edge in the room is guessed, and the guesses will not agree.

The Printable Grids

Every printable sheet in this area carries the horizon at 89 millimetres from the bottom edge on Letter and 85 on A4, a standing viewer's eye level a little below the middle of the sheet. The two-point sheet is the plainest way to see the horizon at work: lay tracing paper over it and place figures with their eyes on the line.

Two-point perspective grid, Letter landscapeDownload PDF
Two-point perspective grid, A4 landscapeDownload PDF

All eight sheets, one per view on each paper, are collected on the perspective overview.

The horizon in a level view carries the points of one-point and two-point perspective; it slides off the frame in three-point and bows in curvilinear perspective. The one rule behind every view is on the perspective overview.

Frequently Asked Questions

What is the horizon line in perspective drawing?: The viewer's eye level carried across the picture as a line. All horizontal vanishing points sit on it, everything above it is seen from below and everything below it from above, and it exists in every picture, including a windowless room, whether or not a real horizon is visible.
Is the horizon line always at eye level?: Yes, by definition. Sitting lowers it, standing raises it, a ladder raises it further. Choosing where to place it in a drawing is choosing where the viewer stands.
Where should the horizon line go in a drawing of a room?: At a standing eye, about 160 centimetres above a floor in a room about 250 high: roughly two thirds of the way down the far wall from the ceiling, a little below the middle of the picture. Higher than that and the viewer is floating.
How do I find the horizon line in a photograph?: Extend two receding edges of one wall until they cross; that crossing is a vanishing point and the horizon passes through it. Or find two standing people of the same height on the camera's ground: if the camera was at eye height, the line through their eyes is the horizon.
Why is there no horizon in my photograph of a tall building?: Because the camera was tilted up. The horizon is still at eye level, but the tilt slides it down the frame and out through the bottom edge. The two horizontal vanishing points are on it, below the picture; the third point, above, is not.
Is the horizon line the same as the skyline or the edge of the sea?: No. The skyline is where buildings meet the sky, at any height. The sea's edge coincides with your eye-level horizon only when you stand at the water's edge; from a cliff it lies well below it. Draw the eye level and let the sea fall where it falls.

Sources

Linear perspective, Encyclopaedia Britannica. Orthogonals, horizon line and vanishing point; the system dated to about 1415 and documented by Alberti in 1435.
On Painting, Book One, Leon Battista Alberti, 1435, translated by John R. Spencer. The centric ray and the construction of the foreshortened floor, the first written one-point construction.
Vanishing point, Encyclopaedia Britannica. The point at which receding parallel lines appear to meet.

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