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3.2 Requirements for embedding charts
We consider two requirements for embedding charts into a Treemap. The
first is the equalization of the scale intervals of charts, and the second is a
change in the size of the drawing area for each chart.
Equalization of axes and their scale intervals:
In general, when we
compare charts that describe the same kind of data, we should assign the
same variable to the same axis. For example, when we compare monthly
precipitation charts of region A and region B, we should assign the months
to the horizontal axis and the amount of rainfall to the vertical axis in both
charts. In addition, the scale intervals of the corresponding axes should be
the same. If the scale interval is different for each chart, it is not easy to
compare their values.
Area efficiency for embedding charts:
We consider that cutting the
upper part of a chart whose maximum value is small does not affect the
ease of comparison. Therefore, when we embed charts into Treemaps
where the filling rate is important, we should change the drawing area
according to the maximum value in the chart. For example, it is
appropriate to embed a chart whose maximum value is large into an area
whose height is large, and vice versa for a chart whose maximum value is
small.
4 Edge-equalized Treemap
In the previous section we discussed some of the problems that Treemaps
present. Based on our considerations, we propose a new type of Treemap,
called an Edge-Equalized Treemap. In this section, we describe its design
principle from three perspectives.
4.1 Equalization of widths
We decided to equalize the widths of the leaf rectangles and use their
height to correspond to the weight of the leaf node (Fig. 6.5). There are
two reasons for our choice. First, we can equalize the scale intervals of
horizontal axes across charts with embedded leaf rectangles. For example,
if the leaf nodes have the same number of data, we can equalize the bar
widths in two or more charts. Second, we can prevent extremely large
margins if we equalize the scale intervals of the vertical axes. For
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