Family tree layout with Dot/GraphViz

Gramps (www.gramps-project.org) generates dot files for family trees, with or without marriage nodes. There is also a way to see this in the Gramps interface itself. http://gramps-project.org/wiki/index.php?title=Graph_View So I would say, look at the output of your family tree as created by Gramps

Try the following:

digraph simpsons {  
  subgraph Generation0 {
    rank = same
    Abraham [shape = box, color = blue]
    Mona [shape = box, color = pink]
    AbrahamAndMona [shape = point]
    Abraham -> AbrahamAndMona [dir = none]
    AbrahamAndMona -> Mona [dir = none]

    Clancy [shape = box, color = blue]
    Jackeline [shape = box, color = pink]
    ClancyAndJackeline [shape = point]
    Clancy -> ClancyAndJackeline [dir = none]
    ClancyAndJackeline -> Jackeline [dir = none]
  }
  
  subgraph Generation0Sons {
    rank = same
    AbrahamAndMonaSons [shape = point]
    HerbSon [shape = point]
    HomerSon [shape = point]
    HerbSon -> AbrahamAndMonaSons [dir = none]
    HomerSon -> AbrahamAndMonaSons [dir = none]
    
    MargeSon [shape = point]
    PattySon [shape = point]
    SelmaSon [shape = point]
    MargeSon -> PattySon [dir = none] 
    PattySon -> SelmaSon [dir = none] 
  }
  
  AbrahamAndMona -> AbrahamAndMonaSons [dir = none]
  ClancyAndJackeline -> PattySon [dir = none]
  
  subgraph Generation1 {
    rank  =  same
    Herb [shape = box, color = blue] 
    Homer [shape = box, color = blue] 
    Marge [shape = box, color = pink] 
    Patty [shape = box, color = pink] 
    Selma [shape = box, color = pink] 

    HomerAndMarge [shape = point]
    Homer -> HomerAndMarge [dir = none]
    Marge -> HomerAndMarge [dir = none]
  }
  
  HerbSon -> Herb [dir = none]
  HomerSon -> Homer [dir = none]
  MargeSon -> Marge [dir = none]
  PattySon -> Patty [dir = none]
  SelmaSon -> Selma [dir = none]
  
  subgraph Generation1Sons {
    rank  =  same
    BartSon [shape = point] 
    LisaSon [shape = point] 
    MaggieSon [shape = point] 
    
    BartSon -> LisaSon [dir = none]
    LisaSon -> MaggieSon [dir = none]
  }
  
  HomerAndMarge -> LisaSon [dir = none]
  
  subgraph Generation2 {
    rank  =  same
    Bart [shape = box, color = blue] 
    Lisa [shape = box, color = pink] 
    Maggie [shape = box, color = pink] 
    Ling [shape = box, color = blue] 
  }
  
  Selma -> Ling [dir = none]
  BartSon -> Bart [dir = none]
  LisaSon -> Lisa [dir = none]
  MaggieSon -> Maggie [dir = none]
}

Produces:

I don’t think you can take an arbitrary family tree and auto-generate a dot file where it always looks good in GraphViz.

But I think you can always make it look good if you:

• Use the rank=same other answers mentioned to get the 'T' connections desired by the OP
• Use the ordering trick Brian Blank did to prevent weird lines
• Assume no second marriages and half-siblings
• Draw only a subset of the tree that obeys the following rules:
  • Let S be the “center” person
  • If S has siblings, make sure S is to right of all of them.
  • If S has a spouse and the spouse has siblings, make sure the spouse is to the left of all his/her siblings.
  • Don’t show nephews, nieces, aunts or uncles of S or S’s spouse
  • Don’t show spouses of siblings
  • Don’t show spouses of spouse’s siblings
  • Show children of S, but not their spouses or children
  • Show parents of S and parents of spouse

This will end up showing no more than 3 generations at once, with S in the middle generation.

In the picture below S=Homer (slightly modified from Brian Blank's version):

digraph G {
  edge [dir=none];
  node [shape=box];
  graph [splines=ortho];

  "Herb"      [shape=box, regular=0, color="blue", style="filled" fillcolor="lightblue"] ;
  "Homer"     [shape=box, regular=0, color="blue", style="bold, filled" fillcolor="lightblue"] ;
  "Marge"     [shape=oval, regular=0, color="red", style="filled" fillcolor="pink"] ;
  "Clancy"    [shape=box, regular=0, color="blue", style="filled" fillcolor="lightblue"] ;
  "Jackeline" [shape=oval, regular=0, color="red", style="filled" fillcolor="pink"] ;
  "Abraham"   [shape=box, regular=0, color="blue", style="filled" fillcolor="lightblue"] ;
  "Mona"      [shape=oval, regular=0, color="red", style="filled" fillcolor="pink"] ;
  "Patty"     [shape=oval, regular=0, color="red", style="filled" fillcolor="pink"] ;
  "Selma"     [shape=oval, regular=0, color="red", style="filled" fillcolor="pink"] ;
  "Bart"      [shape=box, regular=0, color="blue", style="filled" fillcolor="lightblue"] ;
  "Lisa"      [shape=oval, regular=0, color="red", style="filled" fillcolor="pink"] ;
  "Maggie"    [shape=oval, regular=0, color="red", style="filled" fillcolor="pink"] ;

  a1 [shape=diamond,label="",height=0.25,width=0.25];
  b1 [shape=circle,label="",height=0.01,width=0.01];
  b2 [shape=circle,label="",height=0.01,width=0.01];
  b3 [shape=circle,label="",height=0.01,width=0.01];
  {rank=same; Abraham -> a1 -> Mona};
  {rank=same; b1 -> b2 -> b3};
  {rank=same; Herb; Homer};
  a1 -> b2
  b1 -> Herb
  b3 -> Homer

  p1 [shape=diamond,label="",height=0.25,width=0.25];
  q1 [shape=circle,label="",height=0.01,width=0.01];
  q2 [shape=circle,label="",height=0.01,width=0.01];
  q3 [shape=circle,label="",height=0.01,width=0.01];
  {rank=same; Homer -> p1 -> Marge};
  {rank=same; q1 -> q2 -> q3};
  {rank=same; Bart; Lisa; Maggie};
  p1 -> q2;
  q1 -> Bart;
  q2 -> Lisa;
  q3 -> Maggie;

  x1 [shape=diamond,label="",height=0.25,width=0.25];
  y1 [shape=circle,label="",height=0.01,width=0.01];
  y2 [shape=circle,label="",height=0.01,width=0.01];
  y3 [shape=circle,label="",height=0.01,width=0.01];
  {rank=same; Clancy -> x1 -> Jackeline};
  {rank=same; y1 -> y2 -> y3};
  {rank=same; Patty; Selma; Marge};
  x1 -> y2;
  y1 -> Marge;
  y2 -> Patty;
  y3 -> Selma;
}

This yields the following tree by GraphViz (with annotations I added with Power Point):