Multiple keys

It is possible to construct a legend/key manually rather than having the plot titles all appear in the auto-generated key. This allows, for example, creating a single legend for the component panels in a multiplot. Here is an example:

      set multiplot layout 3,2 columnsfirst
      set style data boxes
      plot $D using 0:6  lt 1 title at 0.75, 0.20
      plot $D using 0:12 lt 2 title at 0.75, 0.17
      plot $D using 0:13 lt 3 title at 0.75, 0.14
      plot $D using 0:14 lt 4 title at 0.75, 0.11
      set label 1 at screen 0.75, screen 0.22 "Custom combined key area"
      plot $D using 0:($6+$12+$13+$14) with linespoints title "total"
      unset multiplot