directional line definitionLines can lead the eye in a path around an image. And they can also be used as a powerful way to express something to the viewer. Directional lines express a variety of messages. Diagonal lines, for example, express the sense of energy and give movement to a piece. Horizontal lines, on the other hand, give a piece a sense of calmness and rest. And vertical lines portray structure and strength. Only a single line is necessary to communicate an emotion, whether it be sadness, joy, worry, anger, dejection or exuberance.