The importance of the line in photography

In a photograph (as in a painting) the content is the most important.
Line is one of the essential elements of graphical representation of the content.
There are three categories of lines:
  • straight;
  • curve;
  • broken.
Lines delineate and define surfaces and volumes.
The value of the photographs depends enormously on the shape and orientation of these lines, influencing the overall effect of the photograph on the state of mind of the public. If there is a harmonious and balanced combination of these lines, we will be able to experience a pleasant aesthetical sensation while watching that photograph. 

Straight lines
They can appear in three orientations: vertical, horizontal and oblique.
Depending on their orientation, when they are very long, they can suggest continuity, monotony or pause.

Straight vertical lines
It is a feature of the tall people, trees and high-rise buildings.
In photographs, they suggest dignity, solemnity or some imposing figure. When vertical lines are exaggeratedly long, they suggest a feeling of severity.

Straight horizontal lines
Photographs having dominant lines the straight horizontal lines confer a feeling of calm, peace, endless space, surrender and relaxation.
A frequently recurring example: the horizon line, no matter that it delineates a plain or an ocean.

The abuse of straight lines in photography stresses the monotony sensation, especially when these are parallel lines and no other graphic element intervenes to break the monotony.

Straight oblique lines 
These lines suggest dynamism, especially in the portrait orientation framings. They can be associated with actions like running, falling, etc.
The longest oblique lines are the diagonals (please note that the diagonal of a photographic film frame or of the cmos sensor of digital cameras represents the normal focal length of the respective camera).

Curve lines
Most often, they occur in nature, but of course also in photography, painting and any of the arts, which find their inspiration primarily in nature.
Our mind easily associates curve lines with feminity, grace and winding body movements.
Upwards concavity of the lines in a photograph suggests a joyful and optimistic state of mind, whereas downwards concavity inspires a feeling of sadness or resignation.
A photograph containing curve lines oriented to the left, right or in spiral can suggest fretting, anguish or instability.
Any curve vertical line tends to reach back the horizontal, offering potential energy to the photographic subject.
The "S" curve bears a certain harmony, lightness and appealing esthetic effect about itself, being used in fine arts ever since the Greek Antiquity.

Broken lines
The use of broken lines in photography, no matter if the cinematographic framing - horizontal, or the purely photographic one - vertical, is used, suggests nervousness, hostility or a deployment of energy.
Nervousness is suggested especially when the broken lines are co-occurring more frequently and repetitively.
Any of the visual effects suggested by these lines will be stressed by the acuteness of angles.

Lines to avoid:
chaotically intersecting lines, which are confusing in a photograph;
lines inexplicably and non expressively ending outside the photographic frame.