Stop! Is green greener than yellow?

Friday, March 30th, 2007

There were nice charts in the German journal “Bild der Wissenschaft” 3/2006. They showed risk maps for Germany. Sadly, they weren’t readable. A little trick and they would have been brilliant. A color gradient from dark red via yellow to dark green doesn’t represent a natural order. Neither for the human eye nor for mine. Green is no better, larger or warmer than yellow and yellow no better than red. If colors with identical intensity are used for lowest and highest values you cannot identify patterns.

Earthquake and winterstorm risk Germany

Left: Risk of earth quakes in Germany, right: risk of winter storms, source: CEDIM Risk Explorer

Cognition of colors has to be proportional to displayed values. It’s best with a gray scale. If color is required, different hues of the same color are easily distinguished by the eye. For differentiating positive and negative values a combination of two colors is o.k.

Traffic light vs. color hue

Traffic light colors vs. color hues – geo analysis example from DeltaMaster

What a pity that most designers of weather charts don’t know that, either. Zero degree Celsius is very blue. Plus one degree Celsius is only a little less blue. But never yellow.

weather map

Example of a weather chart

Rich tables for high resolution reporting

Thursday, February 15th, 2007

What is better: tables or charts? That was discussed in the past. Some said a chart is worth a thousand words. I think a picture is worth a thousand words. And most charts need a thousand words to be explained. They are so awful, mostly. Because it is so hard to standardize a chart and there are lots of things that can go wrong. Bissantz loves graphic tables. Me too. Charts are tightly integrated into tables. You have the best of both worlds in one concept. Graphic tables are easy to standardize and you can integrate almost every chart type in a table. Sparklines provide time-series. Horizontal bars are good for almost all types of comparisons. Graphic tables maximize data-to-ink ratio. They are fine grained and with high resolution. The graphical elements provide easy orientation for your eyes. The numbers provide all the details. Typical problems of legends and labeling never arise. I provided some examples in the “Radar chart trap” and in “Small things that make a big difference”. Today, I explain how to create waterfall charts in tables.

A waterfall chart is a variant of a bar chart. It shows how an initial value is changed through other values which lead to a final value. In Excel, you can use invisible columns but this is tricky. Rolf has a nice Excel template for free. Data entry is not so easy. Formatting is very nice.

GM scheme Hichert

Jon has programmed an Excel add-in. Formatting is not so easy. Data entry is very nice.

GM scheme Peltier

In both cases a chart is the result. If you turn it around it is still readable, perhaps even better.

GM scheme turned

Turned around it fits perfectly into a graphic table. Subtotals are also easy. This is how Bissantz has done it in DeltaMaster.

GM scheme in Pivot

It is possible in Excel, too. Just use the REPT function and a few tricks. I show you how in an example Excel sheet.

DB-Scheme inExcel

Radar chart trap

Wednesday, December 6th, 2006

In our company, people think a lot about how to present figures well. ‘Well’ means that everybody is able to quickly grasp what they mean. That gives us more time to brood over their impact.

Things become difficult when it comes to radar charts.

Radar chart

The same data is much better off in a graphical table. The most important fact emerges immediately: I am always above average!

Graphical table

Here at the office, they make software that draws these tables automatically. In Excel you would use the Repeat function. That’s quite simple: a vertical bar is repeated as many times as the corresponding data value prescribes. That yields a nice bar inside the cell. You can even label it if you concatenate the value with the “&” character. Here is a sample how that works.