The viewpoint - the level and angle of the viewer's eye in relation to your subject. How high or low the horizon line is placed determines whether the viewer is looking down, straight ahead or up at the subject.
Your viewpoint indeed makes a difference. A portrait with the face placed high on the picture plane projects force and dignity; one placed lower is approachable and less intimidating.. In an exterior architectural rendering, a low horizon line suggests that the viewer is looking down from above, surveying a scene that is expansive and open, Looking up at the horizon line suggests a more intimate, perhaps introspective scene.
When placing the horizon line, remember that unequal division of space are generally considered the most interesting. Avoid centering the horizon line and the renderings focal point.