Representing Data - Data Points: Visualization That Means Something - page 96

FIGURE 3-4 Scatterplots
One of the advantages of using just position is that it tends to take up less
space than the other visual cues because you can draw all the data within
the x- and y-plane, and you can represent each point with a dot. Unlike other
visual cues that use size to compare values, all points in a position-based
plot are the same size. In turn, you can spot trends, clusters, and outliers by
plotting a lot of data at once.
However, the advantage of using position alone can also be a disadvantage.
If you look at a lot of points at once in a scatterplot, it can be a challenge to
identify what each point represents. Even in an interactive plot, you still must
mouse over or select a point to find out more information, and overlap can
cause more problems.
Length
Length is most commonly used in the context of bar charts. The longer a bar
is, the greater the absolute value, and it can work in all directions: horizontal,
vertical, or even at different angles on a circle.
How do you judge length visually? You figure out the distance from one end
of a shape to the other end, so to compare values based on length, you must
see both ends of the lines or bars. Otherwise, you end up with a skewed view
of maximums, minimums, and everything in between.
As a simple example, as shown in Figure 3-5, a major news outlet displayed
a bar graph on television that compared a tax rate before and after a date.