EDGE-EQUALIZED TREEMAPS - Information Visualisation: Techniques, Usability and Evaluation - page 118

and use a trial and error method. We will arrange the rectangles and
evaluate the results of each layout while changing the parameters. Using
this process, we will be able to obtain a better layout.
5.3 Concrete flow of the process
We show the flow of the process in Fig. 6.6. First, we take as input a
weighted hierarchical structure for each leaf node. The width and height of
the leaf rectangles can then be determined according to their weights.
Second, we repeat the process of filling the rectangles from the leaf nodes
to the root node. After the layout of all the rectangles has been decided, we
adjust the size of the Treemap to the drawing area, and evaluate the result
of the layout with an evaluation function. We then change a parameter and
go back to the process of filling the rectangles. By repeating the above
process, we are able to find the layout that scores best in the evaluation.
Fig. 6.6. Flow of the process
Determination of rectangles for leaf nodes: We determine the width and
height of a leaf rectangle according to the weight of a leaf node. The width
of a leaf rectangle is 1 and the height is proportional to the weight.
Therefore, the proportional constant for determining the height has no
meaning; it is important that the proportional constants are the same across
all leaf nodes.
These widths and heights are provisional until the layout of all nodes
has been decided. They are changed when the Treemap is adjusted to the
size of the drawing area.
Placing rectangles: We treat the problem of fitting child nodes into the
rectangular area of branch nodes as a Strip Packing Problem. The Strip
Packing Problem describes the fitting of rectangles into a fixed-width
rectangular space to minimize the vertical length. We swap the horizontal