Radar graphs in user interfaces

Published on 11^th February 2010 in Usability, Websites, tagged CountryEx, visualisation.

Of the most commonly available methods for visualising data, radar graphs seem to be the least used. When I asked for examples on UXExchange, there were very few that people could think of. So what makes people avoid them and why are they so rare?

Under the radar

When you look at a radar graph, it’s easy to appreciate their limitations. Less than three items and they become useless, but add too many items and they quickly turn into a mess. Although adding elements to a bar graph increases its size in one axis, doing the same to a radar graph forces you to expand its height and width so that it doesn’t become unduly cluttered. The data also needs to be on the same scale for a radar to be used.

Stephen Few explored these deficiencies in an article (PDF) in which he contrasts the relative readability of a radar and bar graph using the same data. As he points out, it’s more difficult to determine the value of each radar graph point because you have to count the number of bars on the axis and compare it to the scale provided. The ordering of the items is also unclear, since the radar has no obvious beginning and end.

In this example, it’s clear that the more commonly used bar graph is far superior to the radar graph and that the latter offers no perceivable benefit. However, this is not the full story.

Effective use in videogames

There’s one place where radar graphs appear far more often than you might expect and that’s in videogames. When I asked for examples on the Thunderbolt forum, I quickly got half a dozen instances of their use. These were not just confined to a particular genre either, but a whole variety of games.

The key difference between the type of radar used in videogames and Stephen Few’s examples is not the type of data that’s visualised, but the level of granularity. In the previous example above, the radar graph is inferior because it’s difficult to compare the absolute values in the data. However, in videogames, radar graphs are not intended to be measured, but are merely an indicator of value.

When radar graphs are used in games, the absolute value of each point is not important. They also have scales which have a finite end and so are always percentages, as opposed to the data used in Stephen Few’s example. This means that you can determine a value by merely glancing at the graph instead of having to understand the scale and use that to estimate the associated value. If the point is about half way along the axis in a game, it’s about 50%. In the previous example above, doing the same is much more difficult.

Other potential uses

In videogames, it’s not the absolute value of a particular point that is important, but the overall size and shape of the graph, which can be recognised quickly. This characteristic lends itself to other applications where monitoring changes is critical. Imagine patient data in a hospital or temperature values in a nuclear power plant. If these were visualised as a radar graph and people learned what the graph’s normal shape and size should be, then spotting changes could be easier than a table of numbers or a bar graph.

Radar graphs in CountryEx

Radar graphs have also proved useful in an interface I’ve been designing. In my university final year project, CountryEx, there are countries which have a number of statistics associated with them. Players of the game need to be able to look at a country’s page and quickly analyse it, but a simple list of numbers doesn’t make that easy.

So above this simple list, I’ve included a radar graph. Like the other examples from games, my graphs have no scale or exact numbers, but are merely an indicator that can be glanced at. The fact that all of the statistics are out of 100 also makes this particularly applicable. In theory, players should now be able to easily check how developed a country is. However, whether this method of visualising information is actually useful will have to be determined by a usability test at a later date.

In conclusion

Although radar graphs may perform poorly when used to represent the majority of data, videogames show that they can be effective. If the information you need to visualise fits within the limitations of radar graphs, then give them a chance.