This algorithm has the following features;

• nodes are placed on layers
• crossings minimization: edge crossings are minimized
• minimum separation: on each layer, neighboring nodes are separated by at least a certain distance
• balance: parents are placed at the barycenter of their children
• proximity: neighboring nodes in the immediately upper layer are placed nearby

For additional material on this algorithm, see:

• Wikipedia; http://en.wikipedia.org/wiki/Layered_graph_drawing
• "Graph drawing and applications" by Kozo Sugiyama, ISBN 981-02-4879-2. Page 29 to 35 gives a description of the algorithm.