# set terminal svg size 600,400 dynamic enhanced fname 'arial'  fsize 10 mousing name "pointsize_1" butt solid 
# set output 'pointsize.1.svg'
unset border
unset key
set style data lines
set noxtics
set noytics
set noztics
set title "plot with variable size points" 
x = 0.0
plot 'world.dat' with lines lt 3,      'world.cor' using 1:2:(5.*rand(0)) with points lt 1 pt 6 ps variable