You should use graphs to demonstrate a point to your audience, especially if they are not expert users. This might mean they are not experts in the subject area or are not used to dealing with data.
The Gestalt principles that we've talked about previously also apply to graphs.
Graphs allow us to organise, analyse and summarise the data. Charts are not good at detail but excellent at:
A great example of the power of charts is.....
All of the above visualisations have the same set of summary statistics:
But they all look very different
Earlier we showed a useful resources for choosing the correct chart. Now we will go through some tips and tricks to help you improve your charts and help get your message across to your users. We will also touch on some ways visualisations can be used to disguise and corrupt numbers. These are things you really shouldn't do, unless you really want to be underhand and sneaky!
These will be light touch as there are plenty of other resources out there. For more in depth chart design then the Office for National Statistics Chart design is a great website to use.
The best advice is to present the data as simply as possible. It’s more important that your user understands your message than using an eye-catching graphic. Below is an example of simplifying a published DWP chart.
Simplification does not mean cutting corners. One of the worst things you can do is accept Excel charting defaults. Below is an example of improving a published DWP chart, which seems to use Excel defaults.
The Washington Post pointed out that Donald Trump loves a bar chart. His election campaign posted more than 40 bar-chart graphics showing favourable poll results. Here's the chart the campaign tweeted in October 2016.
If we add a baseline at the bottom of the graphic, the implied scale doesn't match the numbers
The chart visually inflates Trump's two-point lead to over 11 points. But if we adjust our scale to match the data, where would the baseline end up? If you click the chart above you can see how tall should the bars actually be.....
This is a published DWP bar chart. The improvements show that a bar chart doesn’t really work with small changes in large numbers.
You will notice that the y-axis on the line chart we changed it to also does not start at zero. On a bar chart the consumer is looking at the size of the bars to see what is going on, which is why you can't use a zero baseline. On a line chart the consumer is mostly interested in the trend, so a zero baseline can be used. However, so as not to be at all misleading, a further improvement which we could have made would have been to add a "zoomed out" view of the chart in the corner, to add that extra context in.