The graph area can be divided in two parts.
The margin area
The plot area
These areas can have individual background colors as well as edges of user settable size and color. In addition it is possible to use an image as background with different formatting options.
The plot area is where the plot is drawn and the margin area is everything outside. Methods that affect the format of the plot area are
Graph::SetMargin() , This will adjust the size (and
                                position) of the plot area
Graph::SetBox($aDrawPlotFrame=true,$aPlotFrameColor=array(0,0,0),$aPlotFrameWeight=1),
                                This will adjust tyhe format of the edge around the plot area. By
                                default this is disabled.
In a similar way the margin areas peroperties can be adjusted with the methods
Graph::SetMargin() , same as above 
Graph::SetMarginColor($aColor)
Graph::SetFram($aDrawImgFrame=true,$aImgFrameColor=array(0,0,0),$aImgFrameWeight=1)
Graph::SetFrameBevel($aDepth=3,$aBorder=false,$aBorderColor='black',$aColor1='white@0.4',$aColor2='darkgray@0.4',$aFlg=true)
When auto scaling is used no data points will ever be outside the plot area
                    since the scaling will make sure it covers the dynamic range of the data.
                    However, when setting the scale manually there is always the risk that some data
                    points are outside the specified scale. This could then lead to the result shown
                    in Figure 14.13. Original plot without clipping (  To avoid this situation it is possible
                    to enable clipping to the plot region by calling the methodclipping_ex1.php)
Graph::SetClipping($aFlg)
This will "cut away" all parts of the plot that would otherwise be stroked
                    outside the plot area.Figure 14.14. Plot with clipping enabled (  shows the result
                    after clipping has been enabled.clipping_ex2.php)
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By default clipping is disabled since it will slightly increase the CPU load and the time to generate the graphs.