Overlaying graph links on treemaps

Every graph can be decomposed into a tree structure plus a set ofremaining edges. We describe a visualization technique that
displays the tree structure as a Treemap and the remaining edges
as curved links overlaid on the Treemap. Link curves are
designed to show where the link starts and where it ends without
requiring an explicit arrow that would clutter the already dense
visualization. This technique is effective for visualizing structures
where the underlying tree has some meaning, such as Web sites or
XML documents with cross-references. Graphic attributes of the
links – such as color or thickness – can be used to represent
attributes of the edges. Users can choose to see all links at once or
only the links to and from the node or branch under the cursor.