Data Presentation Styles: Why use Graphs

Why do we use graphs? To make comparisons easier

There is a great range of ways to present data to achieve this goal, often graphic designers use the wrong way because of aesthetic or what’s fashionable. 

An example is the overuse of bubble charts

A chart recreated by Alberto Cairo from a Bloomberg news story, in his book “The Functional Art”

The chart shows the change in market capitalisation of various banks between 2007-2009.

The light grey bubbles represent 2007 and the dark grey bubbles represent 2009.

From this snapshot we can say over the two years their capitalisation cap decreased, all of these banks experienced a fall in their stock price.

The bubble chart is difficult to interpret figures from but looking at the same data in a bar chart it’s much easier to make a comparison and get the estimated figure.

You can make a graph wanting your audience to compare areas but they will automatically compare heights and widths. Using circles always makes us underestimate the size difference.

A ranking of different graphic approaches to compare data

Alberto Cairo, The Functional Art, 2013

Based on human visual perception, as we need to tailor the way that we show stuff. We need to understand the way human perceptions work to decide which way we’ll present data. The more accurate and easier the judgment is for your audience to make, the more likely they’ll take away the correct perception of the patterns you’re presenting.

A case of disastrous use of poorly designed charts is the Space Shuttle Challenger launch accident. 

• Cold weather leading up to launch day at the Kennedy Space Station
• There were discussions between NASA and the manufacturers of the booster rocket about should the shuttle be launched on a cold day.
• The discussion was about the O-rings which sealed the sections of the booster rocket and the possibility of if they would become damaged and unsafe.
• The booster rocket engineers made a no launch recommendation, which was their first no launch recommendation in 12 years.
• They faxed 13 graphics to support their recommendation.

It shows a catalogue of all the earlier launch damage to the booster seals. It’s shown in the historical launch order from 1 to 24. 

The problem is that obscures the two most important variables of interest, the relationship between temperature and the degree of damage. 

• The temperature is shown in the nose of the rockets
• The degree of damage is in the legend in shaded areas

The rocket engineers chose to order their information by time, that is the order of launch not be temperature or degree of damage. This makes the diagrams cluttered and any pattern difficult to see. 

Edward Tufty took that same data and redrew the rocket diagram as a starter plot graph.

Showing the relationship between temperature and O-ring damage. It reveals a clear pattern of damage and severity.

Bar Chart

Easy to use and the audience have a familiarity with them. It makes it quick to compare information and reveal highs and lows at a glance. Effective when you have numerical data across categories.

Line Chart

Connect individual numeric data points. Primary use is to display trends over a period of time.

Pie Chart

Commonly used but also very commonly misused. They are used to show the relative proportions or percentages of information. Limit the number of wedges to 6, if you need more than use a bar chart.

Reflection

In Lecture Pod Five, I learned why we use graphs as well as graphs being overused and not used properly and ultimately leading to disaster. Then the use of particular charts such as bar, line and pie charts are defined.