Contour lines are perhaps the most widely used of any type of line in graphic design, and they are probably what most people think of when they think of graphic lines. A contour line describes a particular shape, object or area. Lines used to create borders around either an individual or series of objects, or define edges are considered contour lines. Contour lines represent the forms of physical objects.
Implied lines are a series of closely bunched points, dots or items that give the appearance of a line. The viewer fills in a continuous, imaginary line that connects these items, as the implied line exists only the in viewer's mind. For example, an image of several cars lined up on the freeway provides the impression of a line, though the cars are not literally touching. A series of bread crumbs or dashes produces the same effect.
Like the implied line, the psychic line exists only in the viewer's imagination and is not drawn. These are assumed or invisible lines and "completed" in the mind's eye of the viewer. An example of a psychic line would be a profile of a person who has her head tilted up, as if looking at something in the sky. The viewer instinctively follows the gaze upward, producing a psychic line. The use of an arrow on a street sign is another example of a graphic designer implementing a psychic line.
These can be drawn in any direction -- horizontal, vertical or diagonal -- but always serve a similar purpose; they divide space. The direction may also influence the message the graphic designer wishes to convey. For example, horizontal lines that divide space promote a feeling of calmness or rest. By contrast, vertical lines are associated with height and give viewers a sense of being alert or at the ready. Diagonal lines are used when a designer wants to provide a feeling of movement or unsteadiness, as if an object is ready to fall.
Gesture lines give the sense of action or movement. Designers that want to give the impression of a person walking or waving are examples of gesture lines. Parallel, straight lines drawn behind the drawing an automobile give it the illusion of moving forwards. A series of nested arcs drawn on one side of basketball makes the ball appear to be rolling. Lines drawn at the top of a chimney gives viewers the sense that smoke is rising.