Whenever we look at a flat surface (a picture, a television screen) and assume we are looking at spaces and objects that have depth, we are accepting a set of visual signals that create an illusion of three dimensional space. 3D cues are so common today that we are almost unaware of them. However, these signals were not always used and understood; even today in some preliterate societies, people may have difficulty understanding 3D illusions. Understanding how these illusions work is a key to developing our ability to think spatially. Spatial concepts come into play whether we are trying to find our way through the streets of a strange town, figure out how to wrap cloth around a body to achieve a fashion idea, envision the inner structures of a complex mechanism or body part, or simply do an accurate drawing of what we see.
The ancient Romans had the ability to depict depth in their paintings. However during the Middle Ages European artists lost the skill of depicting three dimensional illusions accurately. Indeed, this kind of realism was not important for the purposes of visual images in the early Christian era, when figures and landscapes were intended as a kind of generic shorthand for the religious and historical stories being told. Realistic copies of the material world were not valued; instead, stylized symbols of historical and religious subjects were desired, executed in a strictly traditional way that could be easily recognized by a devout, but illiterate, public. As a result, Medieval images like this one were generally flat in appearance, or gave mixed signals about the three dimensional space depicted.
All this changed in the late 15th century, when architects and artists discovered the value and power of three dimensional effects in drawing and painting. This blended with the intellectual explorations of the period, in which truth, realism, and individuality were prized. Three dimensional effects were greeted as a sensational, almost magical illusion that made painting into a kind of magic window into a very believable world. The paintings of Raphael are dramatic examples of the Renaissance fascination with this new bag of tricks. For further information on the history of linear perspective, go to this site and click on Early_history of perspective.
The tools for creating illusions of three dimensional space are overlapping, changing size and placement, linear perspective, relative hue and value, and atmospheric perspective.
The simplest tool for indicating three dimensional space is overlapping. The effect is accomplished by allowing the contour of one form to be interrupted by the contour of another form, so that one supersedes the other. This device can be seen in this Byzantine mosaic as virtually the only spatial cue. The overall composition appears to be quite flat, with only the subtle signal of the overlapping of garments to tell us who is in front and who is farther back. The effect is as if all the people are crowded up against the "window" of the picture- a very flat effect.
The next level of spatial signals is provided by changing size and placement. Placement alone was used earlier, but until changing size was added, the illusion was less than fully convincing, at least to modern eyes.
The greatest leap forward in the representation of three dimensional space occurred in the 15th century, with the discovery of linear perspective. Linear perspective refers to the illusion that objects appear to grow smaller and converge toward a "vanishing point" at the horizon line. The point of convergence may be in any direction the viewer looks, including up, and the horizon/ vanishing point may be visible or imaginary. Paying attention to the shapes of objects in relation to their placement is essential to linear perspective. The rate at which forms appear to change in size and placement is regular, and mathematically predictable. The form (for example, a cube) must also be distorted to suggest perspective. These mathematical discoveries were closely linked to architecture, but also led to a startling new level of realism in drawing, that became the great passion of renaissance artists. In turn, the illusions of linear perspective in drawing led to the creation of innovative spatial effects in architecture.You can go to for a demonstration of linear perspective; or try this link to an interactive example.
Hue and value are very important cues that tell us whether an object is near or far. In general, we tend to read warm hues as being closer that cool hues. We also see colors that are close in value as being close to each other in space, but colors that have strong contrast in value appear to separate in space. Distant objects tend to be either similar or neutral in value, and desaturated in hue. Close objects tend to exhibit stronger, more saturated hues, and/or more contrasting values, including extremes of dark and light. In the landscape shown here, the strongest hue and value contrasts occur where the trees overlap the lake; the trees and sky beyond the lake are no doubt similar in color, but appear to be more neutral in value and desaturated in hue, with less contrast. Also, the warm colors of the leaves in the foreground pull forward, while the cooler colors of the farther shore and the sky tend to recede in distance.
Atmospheric perspective combines several features described above. It operates when objects placed in the upper half of the page, and understood to be far away, lack contrast, detail, and texture. In this painting by Hieronymus Bosch, the upper quarter of the page tends to show less contrast and detail. Not only do the most distant objects tend to be in the upper half of your field of vision, areas intended to be shown as distant will be neither extremely dark or light in value, nor be brightly colored (intense in hue). On the other hand, detail, texture, and hue and value contrast are more likely to appear in the lower half of the picture plane, as they do here.
These qualities are used in combination, as they are in this painting. If any of these concepts is ignored or intentionally set at odds with the others, it interferes with the three dimensional illusion. Here, overlapping, relative size and placement, linear perspective, hue, value, and atmospheric perspective work together to create an illusion of great distance.
It is also possible to break all of these rules purposely in order to create three dimensional illusions that can fool the viewer and/or could never exist in an actual three dimensional model. (Some of the images in this linked site relate to color concepts we will discuss later, not just to spatial concepts)In Chinese art, however, the rules applied to creation of perspective are simply different. Often referred to as "floating Perspective,"in this approach as the viewer's point of view shifts from "near" to "far" parts of the image, the linear perspective point of view also shifts (see this example of floating perspective in Chinese landscape painting..
Other designed objects such as furniture, tools, and appliances must be conceived in relation to function and, often, the contours of the human body that will use the object. Fashion designers face special problems of engineering and spatial thinking, in that the problem is to translate a two dimensional material (cloth) into a three dimensional form (body-shaped garment)-- a unique and complex problem in topographical engineering.
Three dimensional shape has an expressive vocabulary similar to that of line This obviously follows, since line is always implied by the contours of shapes. For example, rectilinear shapes suggest stability.
Angular shapes placed diagonally in relation to gravity suggest instability.
Shapes that exhibit softly curving surfaces suggest quiet, comfort, and sensuality.