"Shadows can express the degree of elevation between surfaces in ways that other techniques cannot. Shadows show the edges of a surface and its degree of elevation against the background. They also make differences in surface elevations perceptible between non-overlapping surfaces

Both a shadow’s size and amount of softness or diffusion express the degree of distance between two surfaces. For example, a surface with a shadow that is small and sharp indicates a surface’s close proximity to the surface behind it. Larger, softer shadows express more distance.

Subtle differences in shadow size and diffusion communicate:

• A detailed degree of distance between two surfaces
• Elevation differences between non-overlapping surfaces"