Velocity is intrinsic to a particle, and doesn't depend on the observer (i.e. the ground is a preferred observer).

Below is a diagram of a person walking above a street on an overpass. The person is headed north, when they see a car driving as shown on the street below. What would the walking person draw for the velocity vector of the car.

 

Since the person is walking to the north, they will observe the car to be moving to the south as well as to the west (i.e. the car is originally north and east of them, but will end up south and west of them). The relative sizes of the southward and westward components depends on the student's interpretation of the relative speeds of the car and the person.