The space covered in a movement can be represented as a function of time. As in this (UNIFORM) movement the space covered and the time taken are proportional: the graph is  always a straight line whose slope is velocity. Regardless of the orientation and direction of the movement, the space covered by the moving body is always positive.
The velocity of a uniform movement can be represented as a function of time. As the velocity does not vary in this type of movement, the graph is always a straight line parallel to the time axis.