Up to this point we have been working in the default graphic units. We now turn our attention to specifying the graphic units that are most convenient for the display of your data values.
The computer screen is, in effect, our viewport into the entire cartesian coordinate system. Only the graphic points that fall within the viewport will be displayed; all other points are eliminated. Lines that cross through the viewport are clipped at the boundaries. The portion of the screen that is to be used to display graphics is specified by the VIEWPORT statement. The CLIP statement allows you to specify clipping boundaries that are different than the VIEWPORT. The SHOW and WINDOW statements specify which portion of the cartesian coordinate system is mapped into the VIEWPORT for display.
