Making Readable Diagrams

Still in light of the subject of the previous post, I really hope that ESAS or anyone else didn’t use 3D pie diagrams, they are the invention of the devil. When still a youngster, I at times worked as a summer intern doing all kinds of graphs and diagrams for a consulting company’s presentations (in good supervision of course) and the basics could be learned quite quickly. Pie diagrams should be always head-on, fully 2D so all sectors having an equal contribution also show an equal area. That’s the whole point with pie diagrams.

There are other general presentation rules too:

  • Don’t put red and green right next to each other since a large percentage of the population is blind to the difference
  • Always have darkness variation besides hue, since it both makes it easier to differentiate and when people print black and white (this WILL be done), the figure is still readable. Also different media always produce variations in color and shade reproduction, it might be that your figures turn out different when they come out in print or in slides, on somebody else’s computer or whatever, when compared to what they look on your screen. So have very clear differences.
  • Try to have the legends in the same order as the lines (in the same vertical order for example)
  • Don’t use colors and shades that are too close to each other. This should be obvious, but apparently is not. There is a huge world of possibilities to differentiate lines in a graph: color, darkness, thickness, line style (solid, dashed, dotted…), markers (dots, lines, stars, pluses, x:s, squares, triangles, empty or filled…). Likewise in areas you can use textures/patterns.
  • Use logical distinctions for different families in a graph. Usually when you plot very many things in a single graph, they can have some groups. Have all NASA numbers have a solid line and all ESA numbers have a dotted line and all Russian numbers have a dashed line. Then you can use black for launch successes and red for failures, same colors for each! For example. Then it’s easy to remember and compare things and you don’t have to cross-reference the legend constantly.
  • Never ever use 3D pie diagrams. They suck. You can put the sectors you want to appear as big in front. They are the devil’s invention, intended to confuse, misrepresent and mislead and are not illustrative or clear.
  • In stuff that has adjacent colored areas, like pie diagrams and cumulative line/area diagrams, use sufficient alternating darknesses to differentiate between the areas. That makes it easy to read. If you put light red and light purple next to each other, since you think you’re running out of colors, it’s hard to discern them. Use the light purple somewhere else and put a dark color next to the light red. It doesn’t matter too much in this case if there are colors in the figure that are that similar as long as they don’t touch each other (remember though if some areas go to zero then the areas on both sides seem to touch each other) and the legend is clear in showing which is which. (Legend ordering helps here.)

You can see many of the rules being violated here, in a lesson on pie diagrams where the diagrams often have dark areas next to each other. At least they use 2D pies. Another example of many charts with some mistakes is this lesson from Australia. The identification of particular violations of the above points is an exercise left to the reader, although the lessons in general have lots of good stuff as too. 🙂

I hope that any rocketeers or scientists reading this blog can take my rants as good advice and enable you to perhaps make perhaps presentations in the future. I’m sorry I didn’t have time to make any illustrations now.

To mellow the whole unpleasant tone of the post, NASA does make some good charts too. 😉 EDIT: it seems the Titan 2 is quite thick compared to the Titan 4? I wonder if all the data is correct….

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