Here's a video that continues the XY chart ideas in my previous postings. (Sorry for really bad blurring. Anyway, as crappy as this video is, you can see the idea.)
This sample hierarchical system (hierarchical graph) consists of 25 thousand parts in maximum eight levels. It allows me to drill-down from any branch (only one branch is open at each level). When I return to an upper level, all lower levels and nodes under it disappear and new branching starts.
Here's a better image:
This graph user interface is contextual. It's the only practical way to display large graphs in a limited space such as on a computer screen. It only shows the related nodes around the selected one. Following this principle, in a non-hierarchical graph you can display nodes linked to the central node, as well as the nodes linked to them (1st and 2nd level links). When you click a node, the clicked node becomes the central one, etc.
This kind of user interface is good for exploring large organization structures (or any hierarchical graphs). Since the system relies on the idea of drilling-down (actually, self-drilling), it's well possible to display extra information (tables and charts) about the currently selected node near the hierarchy tree (under it or to the right of it).
Technically, to calculate (x, y) coordinates, each hierarchy node has to know its level, the max number of levels, the order within its siblings (between 1...n), and the number of siblings (n).
x = my sibling id / number of siblings - 1 / (2 * number of siblings)
y = 1 - (my level / max number of levels)
The lines between nodes are drawn with the same kind of principles as in my previous postings.