Rates can be described mathematically and graphically. Graphically, rates are represented by arrows, whose length equals the magnitude of the rate and whose orientation on an axis represents the direction in which the object at that rate is moving. These arrows are called vectors. Vectors have both magnitude and direction, and therefore describe rates, such as velocity and acceleration. If a property can be described graphically but does not have a direction it is called a scalar.
Scalars have magnitude but no direction, such as time, mass, and temperature.
Actually people use both. Scientists first calculate velocities for each GPS site in centimeters per year, using mathematical equations. Then, they place the velocities, in the form of vectors, on a map of the Earth. This allows them to get a better mental picture of what is happening to the plates world wide. These velocity maps can be made for any area where the displacement of a set point over a period of time is known.