EDGE-EQUALIZED TREEMAPS - Information Visualisation: Techniques, Usability and Evaluation - page 121

6.1 Widths of borders
As with many other Treemaps, we vary the thickness of borders to make it
easier to distinguish the parent-child relationship of nodes.
We draw the nodes of shallow levels with a bold border and the nodes
of deep levels with a thin border (Fig. 6.9). In other words, the border of a
root node is the boldest and the borders of leaf nodes on the deepest level
are the thinnest. This allows us to distinguish the hierarchy without
confusing the borders of other levels.
Fig. 6.9. The differences in border thickness
6.2 Colours of rectangles
We use colours to enhance the recognition accuracy of nodes. In this
research, hierarchical structures have weights in their leaf nodes alone.
Because of this, we devised a separate representation for leaf nodes and
branch nodes.
6.2.1 Leaf rectangles
We assign a different colour to each leaf rectangle to make the separation
among rectangles easy to see. However, we know it is difficult to find
parent-child relationships. When branch nodes that have the same parent
are given different hues, their closeness is weakened.
Because of this, we give leaf nodes with the same parent similar hues.
Conversely, we assign dissimilar hues to leaf nodes from different parents.
For example, the children of one branch node are assigned a red-tinged
colour, whereas the children of another branch node are given a blue-
tinged colour.
With the above procedure, it becomes easy to recognize which leaf
node belongs to which parent node. In addition, this colouring allows us to