A contour drawing is a drawing made up of lines. These lines should outline and make up the object that is being drawn.
Variation of thickness of lines in a drawing affect how the drawing is viewed by a viewer. Lines that are thicker appear closer to the viewer and lines that are thinner seem farther away from the viewer.
When talking about composition, there are three different types of lines. These three types are actual line, implied line, and imaginary line.
Hatching is when the artist uses multiple lines in close vicinity for the appearance of shading.
Pixelation can cause a curved line to appear like a bunch of blocks put together. This can be solved by using antialiasing, which is the color conversions of the pixels surrounding the lines to make it appear less block like.