Horizon line: The farthest point we can see where the delineation between the sky and ground becomes distinct. The line on the picture plane that indicates the extent of illusionistic space and on which are located the vanishing points. In the picture above the horizon line can be seen where the snowy land and trees meets the sky.
Juxtaposition: When one image or shape is placed next to or in comparison to another image or shape. In the picture below, the polaroids have been "juxtaposed" together to create the image of the man.