Final answer:
The thin black lines on a graphic SID typically depict contours or edges. These lines are used to outline figures and forms in an image, creating the illusion of shading and form.
Step-by-step explanation:
The thin black lines on a graphic SID typically depict contours or edges. These lines are used to outline figures and forms in an image, creating the illusion of shading and form. They help make objects look three-dimensional and give a sense of depth. In addition, lines can also be used to show shading and shadows caused by light hitting one side of an object, leaving the other side in shadow.
For example, closely spaced lines called hatching can be used to show that a certain area is in shadow. Lines are also used to create motion and imply movement in a picture.
Overall, lines play an important role in creating visual effects and conveying information in graphic SIDs.