Crate the data set. The data set SWIRL is generated data that produces a symmetric contour pattern, which is useful for illustrating the pattern option.

data swirl; 
    do x= -5 to 5 by 0.25;
       do y= -5 to 5 by 0.25;
          if x+y=0 then z=0;
             else z=(x*y)*((x*x-y*y)/(x*x+y*y)); 
          output; 
       end; 
    end; 
run;