The pad attribute specifies how much, in inches, to extend the drawing area around the minimal area needed to draw the graph. If the pad is a single double, both the x and y pad values are set equal to the given value. This area is part of the drawing and will be filled with the background color, if appropriate.

Normally, a small pad is used for aesthetic reasons, especially when a background color is used, to avoid having nodes and edges abutting the boundary of the drawn region.