The horizon / eye level is the axis around which a perspective drawing is constructed.

When we are outdoors we use the horizon as a point of reference to judge the scale and distance of objects in relation to us.

In perspective drawing, the horizon happens to be the viewer's eye-level.

In art, we tend to use the term 'eye level', rather than 'horizon' as in many pictures, the horizon is frequently hidden by walls, buildings, trees, hills etc.

To create the perspective drawing above we have added some tourists to our scene from page 1.

Note how all four figures share the same eye level - i.e. the horizon of the picture. This suggests that they are all the same height and are standing on the same plane. Because the horizon happens to be our eye level, it also suggests that the figures are the same height as any viewer of the picture. As a result, the organisation of scale and distance in the drawing makes good visual sense.

If you mouse over this drawing it should reveal our second image. Although the figures are still the same size, their eye levels no longer have any relationship to the eye level of the picture. As a result, the scale of the figures is totally confused.

This demonstrates the importance of the horizon / eye level to the organisation of scale and distance in a perspective drawing.