In earlier versions of gnuplot, some terminal types used the values from size to control also the size of the output canvas; others did not. The use of 'set size' for this purpose was deprecated in version 4.2. In version 4.4 almost all terminals now behave as follows:
`set term <terminal_type> size <XX>, <YY>` controls the size of the output file, or "canvas". Please see individual terminal documentation for allowed values of the size parameters. By default, the plot will fill this canvas.
`set size <XX>, <YY>` scales the plot itself relative to the size of the canvas. Scale values less than 1 will cause the plot to not fill the entire canvas. Scale values larger than 1 will cause only a portion of the plot to fit on the canvas. Please be aware that setting scale values larger than 1 may cause problems on some terminal types.
The major exception to this convention is the PostScript driver, which by default continues to act as it has in earlier versions. Be warned that the next version of gnuplot may change the default behaviour of the PostScript driver as well.
Example:
set size 0.5, 0.5
set term png size 600, 400
set output "figure.png"
plot "data" with lines
These commands will produce an output file "figure.png" that is 600 pixels wide and 400 pixels tall. The plot will fill the lower left quarter of this canvas. This is consistent with the way multiplot mode has always worked, however it is a change in the way the png driver worked for single plots in version 4.0.