# set terminal pngcairo  background "#ffffff" enhanced font "arial,10" fontscale 1.0 size 600, 400 
# set output 'pointsize.1.png'
unset border
unset key
set style data lines
set noxtics
set noytics
set noztics
set title "plot with variable size points" 
plot 'world.dat' with lines lt 3,      'world.cor' using 1:2:(5.*rand(0)) with points lt 1 pt 6 ps variable