Vector Definition Mathematically, a vector is a quantity, defined by both magnitude and direction. For example, a vector could be illustrated by an 1 inch arrow pointing at a 30 degree angle. Another vector may be 2.5 inches and point at a 160 degree angle. In the computer world, vectors are used to define paths in certain types of images, such as EPS files and Adobe Illustrator documents. These images are often called vector graphics since they are comprised of vectors, or paths, instead o...