This data type is called a border since it was originally used to create
border lines around display objects.  It is actually a general purpose
structure for drawing connected lines between any series of points.

A border is easier to use than an image structure.  only the following
need be specified to define a border:

  * An internal position component which is used in determining the final
    position of the border.

  * A set of coordinate pairs for each vertex.

  * A color for the lines.

  * One of several drawing modes.

 border structure definition     border colors and drawing modes 
 directly drawing the borders    border coordinates 
 border example                  linking borders