Syntax:
set terminal imagen {<fontsize>} {portrait | landscape} {[<horiz>,<vert>]}
where fontsize defaults to 12 points and the layout defaults to landscape. 4#4horiz5#5 and 4#4vert5#5 are the number of graphs in the horizontal and vertical directions; these default to unity.
Example:
set terminal imagen portrait [2,3]
puts six graphs on the page in three rows of two in portrait orientation.