In a landscape all the subjects we have studied in isolation are brought together: plants and animals, people and buildings; but the determining factors in a landscape are the form of the earth's surface, and the sky above it with its colors, clouds, mists and stars.
As with all solid things, the form of the earth can be made intelligible only through the medium of perspective. Linear perspective is the principal means, with its reduction in the scale of things as they approach the horizon. But a straight path with its sides running to a vanishing point indicates space and distance whether the land is rising or falling away. As in drawing buildings it must be related to other lines running parallel to it.
If the path winds or rises and falls alternately it implies the rise and fall of the surrounding land. If it disappears and rises again the reduction in its breadth when it reappears shows how far away it has now run from the beholder, how far the landscape stretches. Fields and patches of woodland are useful in the same way because of the deviation from normal perspective caused by the undulations in the ground.
If a small tree is drawn near to a large one of the same kind, the effect will be to imply distance between them, although in fact trees of the same species can vary greatly in size. To make the real difference in size clear, the foliage of both trees must be given with the same texture and shown to be of the same size, for the size of leaves does not vary with the size of the tree.
Even though all the usual methods of perspective can be used to give an illusion of space and distance - gradations of size, heavy drawing against faint, dark areas against light - it is impossible for the earth formation by itself to give an indication of the scale of the scene. Even trees, as has just been shown, cannot always serve to do this.
Only accessories of clearly defined size can perform this function unequivocally, such as people and animals, or buildings, which are always related to the human scale by the size of their windows and doors. Very often figures are added to a picture at the end to give the scale of the landscape. It is amusing to recall how in the Baroque period many landscape painters had to employ specialists to put in the figures for them, as they could not manage them themselves. Two examples in the illustration show the same earth formation with a different scale indicated by a single feature, the duck in one, reducing it, and the boat in the other, enlarging it.
Shadow perspective can also be ambiguous in a landscape. Cloud shadows are deceptive, and towards the horizon the haze of the atmosphere completely eliminates the modeling of mountain, tree or building. A mountain mass of great depth looks like a wall, trees become as flat as stage scenery, and the sea of houses in a distant town is nothing more than a flat silhouette. But the outline of a silhouette is sharpened by distance and the illusion of recession in space is associated with it. The same impression arises whenever these outlines become less clear, as through a mist or flickering light.