a value between 0 to 1, specifying the effective size of the circle plot area in the current window. The smaller the size, the larger the blank area around the circle plot.
oma
A vector of the form c(bottom, left, top, right) giving the size of the outer margins in lines of text.
mar
A numerical vector of the form c(bottom, left, top, right) which gives the number of lines of margin to be specified on the four sides of the plot.
Details
After setting up, the extremes of the user coordinates of the plotting region can be found out by par('usr').