Vectors are directional forces that lead our eyes from one point to another in a picture or a shot. Basically, there are three main different types of vectors:
Index vectors are the most obvious type, as they take the form of something in the shot that is clearly pointing somewhere, such as a one-way sign.
Motion vectors are created by elements in the shot that are moving in a certain direction, such as a bus driving left to right across the shot.
Graphic vectors take the form of aspects in a scene that have a directional element, such as skyscrapers in a city or a sidewalk cutting through the shot.