Databases Reference
In-Depth Information
1200
Figure 3.5:
A modern altimeter encoding a single value across a linear axis (Redrawn from
Spence, R.
,
2007
).
Figure 3.6:
A color scale in which each color is lighter then the previous one.
happen: it will be up to the presentation phase to deal with such an issue. On the other hand, some
aggregation
operation can assist the visual analysis: Figure
3.7
(b) shows the frequency distribution
of the topic' page numbers and Figure
3.7
(c) shows a box plot (
Tukey, J.
,
1977
) of the same data.
Likely, the most used representation of bivariate data is the scatterplot. Figure
3.8
shows the
books of Figure
3.7
plotted by publication year (
y
-axis) and number of pages (
x
-axis). A quick glance
reveals that the bigger topics (more than 1000 pages) have been published after 1990, and that few
topics are older than 1976. In some domains, like medical, climate studies, or market analysis, one
of the two attributes is the time, and the other one is a value that changes over time; in such cases,
typical time series diagrams are used (see Figure
3.9
). However, when the observed time ranges over
cyclic periods (e.g., the hours of several consecutive days), some interesting alternatives do exist,
allowing for easily comparing the periodicity of some behaviour. As an example, Figure
3.10
(a)
shows a company network traffic among several days. Each concentric circle represents a day, while
