Line and Shape
One of the most common uses of line is to define shape. We can draw circles, squares, triangles, etc. it gets really interesting when we begin drawing contour lines. I have always thought of contour lines as the outline of something. Out of curiosity I looked up the definition and found it interesting. One definition said, "a line connecting points of equal elevation." This is of course referring to contour lines on a map, but if we take the idea and apply it to drawing it makes one think. Contour lines when grouped together are meant to show elevation changes or depth, but a single contour line is actually flat. When we look at contour line in drawing as the outline of something, it is flat. It's a silhouette. There is no space, no depth. Despite this lack of depth, a well drawn contour line will still define the shape and communicate ideas, and even emotion. And of course you play with perception in fun ways. This optical illusion is a classic for teaching perspective...