Example from Stack Overflow: http://stackoverflow.com/questions/7374108/graphviz-node-placement-and-rankdir
[[[ @dot digraph gex4 { ranksep=0.2;
node[shape=box3d, width=2.3, height=0.6, fontname="Arial"]; n1[label="Incident Commander"]; n2[label="Public Information\nOfficer"]; n3[label="Liaison Officer"]; n4[label="Safety Officer"]; n5[label="Operations Section"]; n6[label="Planning Section"]; n7[label="Logistics Section"]; n8[label="Finance/Admin. Section"];
node[shape=none, width=0, height=0, label=""]: edge[dir=none]; n1 -> p1 -> p2 -> p3; {rank=same; n2 -> p1 -> n3;} {rank=same; n4 -> p2;} {rank=same; p4 -> p5 -> p3 -> p6 -> p7;} p4 -> n5; p5 -> n6; p6 -> n7; p7 -> n8; } ]]]