Been trying to figure out the big maps, all 255 nodes in their x,y locations. Can not figure which attribute(s) need tweaks to get anything like the ...GalaxyO[0-7] vector maps. Niiiice.
Using ... -Kneato ... or maybe ... model=mds ... getting slightly legible maps with just a tiny subset eg. 0,19,71,75 nodes but dot wants to render what Dot Matrix plots.
AFAIK you specify a graph (which means nodes and edges), and graphviz will automatically layout the graph in a (meaningful) way.
But if you already know x and y coordinates you do not need that layout algorithm at all.