You can position the key legend manually in most plotting programs. For example, in gnuplot it's done using set key top right. In ggplot2, it's done like this.
Is there a plotting library, script, or simple algorithm that automatically positions the legend such that it overlaps the data in the plot minimally?
What I mean is: Suppose I plot the line y=x. A good place for the legend in that case would be top left or bottom right.
Try this,
require(Hmisc)
?largest.empty
there are other discussions and functions proposed in R-help archives