GUI Design

http://stackoverflow.com/questions/42793/gui-design-techniques-to-enhance-user-experience

A figure like http://www.adaptive-planning.com/images/mpp.jpg would be quite explanatory about the functionality of the GUI.

Audacity is an open source GUI using wxWidgets. The source can be useful in constructing our GUI.

PAC + MVC + Mid-way Pull-Push model.

For visualization, can use force-directed layout. VTK. has vtkGraphLayoutView. The excellent Boost.Graph library provides a wide range of algorithms, among which a few layout algorithms. I'd recommend using either Kamada-Kawai spring layout or Fruchterman-Reingold force-directed layout. neato from graphviz also implements force-dir layout. This guide includes using the fdp layout algorithm, which appears to be exactly what you want. All of graphviz falls under the Common Public License.