One way to make the graph more usable is by having tools to create visual hierarchy. One way to do that is by having options to visually distinguish between various types of nodes.
- Color is one way.
- Level of opacity could be another.
- Shape of the nodes could be another.
Currently, the nodes are represented as circles. There could be an option to change the shape of nodes, in the same way you can change their color.
For instance, I might choose to display MOCs (Maps Of Content) as squares instead of circles.