Perspective

Linear perspective is a method of portraying objects on a flat surface so that the dimensions shrink with distance. The parallel, straight edges of any object, whether a building or a table, will follow lines that eventually converge at infinity. Typically this point of convergence will be along the horizon, as buildings are built level with the flat surface. When multiple structures are aligned with each other, such as buildings along a street, the horizontal tops and bottoms of the structures will all typically converge at a vanishing point.


Two-point perspective drawing.

When both the fronts and sides of a building are drawn, then the parallel lines forming a side converge at a second point along the horizon (which may be off the drawing paper.) This is a "two-point perspective". Converging the vertical lines to a point in the sky then produces a "three-point perspective".
Depth can also be portrayed by several techniques in addition to the perspective approach above. Objects of similar size should appear ever smaller the further they are from the viewer. Thus the back wheel of a cart will appear slightly smaller than the front wheel. Depth can be portrayed through the use of texture. As the texture of an object gets further away it becomes more compressed and busy, taking on an entirely different character than if it was close. Depth can also be portrayed by reducing the amount of contrast of more distant objects, and also by making the colors more pale. This will reproduce the effect of atmospheric haze, and cause the eye to focus primarily on objects drawn in the foreground.