Line is considered an element of art because it is a fundamental building block in visual art. It can be used to create shapes, forms, and textures, and it can also convey movement, direction, and emotion. In art, lines can be straight, curved, thick, thin, or even implied. They can be used to define boundaries, create patterns, or lead the viewer's eye through a composition. Overall, line is a crucial element that artists use to communicate and express their ideas visually.