Monday, April 2, 2007

Red sunsets and air quality--what chart to use?

Spring is two weeks early in Southern Finland. Ice and snow has melted, brooks and rivers are full of water, birds migrate north over the Gulf of Finland, and sunsets are beautiful reddish.

Red sunsets? They might please the eye, but also make my eyes itch when riding my bike. The red color is in fact caused by numerous air pollutants: small particles released from snow and spread all over by traffic, also from burning branches and trees. I'm waiting a heavy rain to wash the dust away.

(Aside: The Japanese flag represents the rising red sun, probably designed thousand years ago. Did the designer live in a village where people burned a lot of tree in wintertime? Did he or she understand our modern age will see in the flag a proof of air pollution?)

I'm slowly getting towards my point, data visualization, one of my key interests :)

Since the air quality is a worry to people nowadays, the largest newspaper in Finland, Helsingin Sanomat, published the following chart a few days ago.
Air quality in three different places during recent five days
Is the data output well designed? Not at all.
When air quality is good, bars are short; when bad, long. Yep. I'm able to get the information but still, the BAR CHART makes me ask in what sense bad air should be "longer" or "more" than good air?

Another thing, there are colored bands in the background to tell the air quality in words: good, satisfactory, so-so, bad, very bad. The bands for satisfactory and so-so are narrower than good and bad, while very bad is a much wider band than others. Why? Does that carry some message I should understand?

A probable explanation: The graphic designer gets exact figures of air pollutant concentrations every day. Color bands are concentration ranges defined by health care authorities. When drawing the chart, the designer hides exact numbers and adds color bands to correspond the good, satisfactory, so-so, etc air quality ranges.

But we humans don't think like this!
To us the air quality is either good or bad (or something between the opposites) without having to think which extreme is "more" and which is "less". The scale is irrelevant as soon as you can understand changes over time.
Below is my proposition how the newspaper should do it (the data is partially my imagination such as forecasted rains starting tomorrow).

In this presentation of two charts, air quality is no more a separate phenomenon but comparable to temperature and precipitation (which indeed influence the air quality). A line chart displays changes in air quality clearly. A longer period helps readers put the current air quality in context.
Much better than the original, don't you think?
How about you? Do you also share the same passion to enhance charts and tables printed in daily papers? :)