The use of lines is an effective way to add structure to an image. Lines are apparent in the distinction between light and dark, especially at the edge of the subject seen against the background and in the limbs.
Strong lines are powerful compositional elements that suggest to the viewer where they will look. A dominant line that draws our eye, such as a distinct horizon or roadway, is at times called a line of force, guiding line, or leading line.
In the image below, the lines of perspective converge on the model. Notice how the lines align with the lines of the body. The lower edge of the back railing lines up with the model’s arm and the upper edge lines up with her elbow. The edges of the slab on which she is lying line up with the interior lines of her figure.