set multiplot
and then changing the margins let you freely modify the position of all your graphs and customize the distance between them. If you want four graphs on top of each other similar to what you showed in the link, you could do something like the following:
set multiplot
set lmargin at screen 0.2 # Sets left margin at 0.2 from left end
set rmargin at screen 0.9 # Sets right margin at 0.9 from left end
set tmargin at screen 0.9 # Sets top margin at 0.9 from bottom
set bmargin at screen 0.7 # Sets bottom margin at 0.2 from bottom
set format x '' # Remove numbers along x axis
plot sin(x)
set tmargin at screen 0.7 # Sets top margin at 0.7 from bottom
set bmargin at screen 0.5 # Sets bottom margin at 0.5 from bottom
plot cos(x)
set tmargin at screen 0.5 # Sets top margin at 0.5 from bottom
set bmargin at screen 0.3 # Sets bottom margin at 0.3 from bottom
plot exp(x)
set tmargin at screen 0.3 # Sets top margin at 0.3 from bottom
set bmargin at screen 0.1 # Sets bottom margin at 0.1 from bottom
set format x # Restore numbers along x axis
plot x**2
And of course you can complicate this as much as you want.