Cluster relations in a graph can be highlighted using gvmap.

This is a co-authorship graph. Each node is an author and an edge exist between two authors if their name appears in a paper on one of the International Symposium on Graph Drawing bwteeen 199\ 4-2007. The top 8 connected components is taken, and the graph is laidout using sfdp. A map showing the clustering relationship is generated using gvmap.

Note that input graph to gvmap must first be laid out, with overlap removed. E.g.,

sfdp -Goverlap=prism -Gcharset=latin1 gd_1994_2007_8comp.gv | gvmap -e | neato -Ecolor="#55555522" -n2 -Tpng > gd_1994_2007_8comp.png

More information about the algorithm behind gvmap is found here.