title: How to control the igraph plot layout with Fixed Positions?
body: <p>I am trying to draw a network visualization to resemble a flow diagram.  I'm fairly close with the following code, but I have a couple questions:</p>
  
  <ol>
  <li>Is this the best layout() algorithm, or can I manually assign a position for each node></li>
  <li>How can I make sure that these nodes don't overlap in the plot (as they do here)?</li>
  <li>Can I assign one node as an "anchor" or starting point?  i.e., can I make "C" the top-most or left-most node?</li>
  </ol>
  
  <p>Thanks so much!!</p>
  
  <pre><code>library("igraph")
  L3 &lt;- LETTERS[1:8]
  d &lt;- data.frame(start = sample(L3, 16, replace = T), end = sample(L3, 16, replace = T),
                  weight = c(20,40,20,30,50,60,20,30,20,40,20,30,50,60,20,30))
  
  
  g &lt;- graph.data.frame(d, directed = T)
  
  V(g)$name 
  E(g)$weight
  
  ideg &lt;- degree(g, mode = "in", loops = F)
  
  col=rainbow(12) # For edge colors
  
  plot.igraph(g, 
    vertex.label = V(g)$name, vertex.label.color = "gray20",
    vertex.size = ideg*25 + 40, vertex.size2 = 30,
    vertex.color = "gray90", vertex.frame.color = "gray20",
    vertex.shape = "rectangle",
    edge.arrow.size=0.5, edge.color=col, edge.width = E(g)$weight / 10,
    edge.curved = T, 
    layout = layout.reingold.tilford)
  </code></pre>