The HPGL language does not contain any polygon primitives. GPHIGS simulates all polygon filing on this driver.
HPGL II adds this kind of functionality. Use HPGL II when possible for applications which requires polygon filling.
The size of the plot can be redefined by setting the %ds directive. In this case, any workstation type will give the same result. the size will be taken from the %ds directive.
The phigs.h include file contains useful defines for workstation types.