Depth/Dimension/Space

Here is an example of Google Earth's street view on the Golden Gate Bridge. As it is a 2D representation of 3D, we can make out certain elements within dimension to create a depth perception. Use of overlap of a speed limit sign in front of a line of cables show depth acting in space. The parallel lines of the sides of the bridge converge into a vanishing point. And the eyes are deceived as thought they were peering into a distance although all there really is a horizon where all lines tend to meet at the vanishing point. The lines of cables get smaller showing scale to create more depth to allow us to perceive space. These make use of relative height and size. They create a certain texture gradient as well.

http://earth.google.com/intl/en_uk/userguide/v5/images/street_view.jpg