Perspective: the science of painting and drawing so that objects represented have apparent depth and distance…The Merriam-Webster Dictionary

In the painting Gare du Nord several different techniques are used to achieve the illusion of depth or Perspective.

Objects closer to the viewer have more detail and are modeled with highlights and lowlights to create the illusion of depth. Objects in the background are less detailed and slightly out of focus. When color values in the foreground are brighter and warmer and color values in the distance are cooler and of a lesser intensity the viewer perceives the brighter warmer colors to be closer. These techniques combine to make up Atmospheric Perspective.

Linear Perspective is when parallel lines converge to a vanishing point at the horizon or eye level.  Another technique is to have objects overlap to demonstrate depth or have objects become smaller as they are placed further back in the picture plane and the spaces between objects diminish proportionately with the desired depth.

All of these elements combine in a work of art to create the illusion of distance and depth, Perspective.