tips for creating Graph diagrams

Question

I\'d like to programmatically create diagrams like this
_{(source: yaroslavvb.com)}

I imagine I should use GraphPlot with VertexCoordinateRules, Verte

Answer 1

For simple examples where you are only connecting two nodes (like your example on the far right), you can draw lines with capped end points like this.

vertices = {a, b};
Coordinates = {{0, 0}, {1, 1}};
GraphPlot[{a -> b}, VertexLabeling -> True, 
 VertexCoordinateRules -> 
  MapThread[#1 -> #2 &, {vertices, Coordinates}], 
 Prolog -> {Blue, CapForm["Round"], Thickness[.1], Line[Coordinates]}]

For more complex examples (like second from the right) I would recommend drawing a polygon using the vertex coordinates and then tracing the edge of the polygon with a capped line. I couldn't find a way to add a beveled edge directly to a polygon. When tracing the perimeter of the polygon you need to add the coordinate of the first vertex to the end of the line segment that the line makes the complete perimeter of the polygon. Also, there are two separate graphics directives for lines CapForm, which dictates whether to bevel the ends of the line, and JoinForm, which dictates whether to bevel the intermediate points of the line.

vertices = {a, b, c};
Coordinates = {{0, 0}, {1, 1}, {1, -1}};
GraphPlot[{a -> b, b -> c, c -> a}, VertexLabeling -> True, 
 VertexCoordinateRules -> 
  MapThread[#1 -> #2 &, {vertices, Coordinates}], 
 Prolog -> {Blue, CapForm["Round"], JoinForm["Round"], Thickness[.15],
    Line[AppendTo[Coordinates, First[Coordinates]]], 
   Polygon[Coordinates]}]