Hidden line

In mathematics, a hidden line is a geometric edge line that is not visible from an observer's view of a shape or object.

A common practice is to draw the visible edges as solid lines and the hidden lines as dotted lines, dashed lines, or thinner lines than the visible lines.

Hidden lines can help visualize geometric objects in three-dimensional space. Hidden lines add geometric information about the unseen sides of an object.

A three-dimensional object drawn with solid visible and hidden lines is a wire-frame model of the object.