Combine several graph layouts (that already have layout information). Graphviz filters:
acyclic,bcomps,comps,edgepaint,gvcolor,gvpack,mingle,nop,sccmap,tred, &unflatten. More information: https://graphviz.org/pdf/gvpack.1.pdf.
gvpack {{path/to/layout1.gv path/to/layout2.gv ...}} > {{path/to/output.gv}}
gvpack -g {{path/to/layout1.gv path/to/layout2.gv ...}} > {{path/to/output.gv}}
gvpack -n {{path/to/layout1.gv path/to/layout2.gv ...}} > {{path/to/output.gv}}
gvpack -u {{path/to/layout1.gv path/to/layout2.gv ...}} > {{path/to/output.gv}}
gvpack -?