Monthly Archives: Aug 2021

Embrace diversity – how to design data visualizations for people with visual impairments.

Have you ever thought that it is possible to discriminate people through data visualization design? Several years ago, it sounded strange to me too, but indeed, it can be done unconsciously if you are not aware of the topic.

Discrimination is most often associated with skin colour, gender, age, religious beliefs, or nationality. However, this negative social phenomenon can have much broader spectrum. One of them, not at all intuitive, is data visualizations practices. The topic is gaining importance as more and more data is used to explain global processes, and those with difficulties in that area are being left behind. It may not be simple, but the onus is on data community and data visualization practitioners to develop new best practices to communicate data in more democratic way with those with difficulties in this area in mind.

To make data visualization more accessible to a wider audience, three dimensions can be improved: vision, cognitive and learning difficulties, and motor capabilities. The basic, obvious difficulty is related with vision impairments; but the degree of impairment is key. I will not discuss the most severe degree, which is blindness (this is a topic for different post), but I will bring closer the subject of colour-blindness and low vision impairments.


In data visualization, colour is the most important communication channel. The ability to see and understand the meaning of colours helped our ancestors to survive in deep jungles or on savannas. Colour informed them about non-toxic food or allowed them to spot predators in the forest.

Today, we are still sensitive to colours and these naturals reactions are used in many ways. For instance, most warning signals use red colour, because we naturally associate it with danger or action (red is a colour of the blood)[1]. Studies show that prolonged exposure to the red colour can cause the heart rate to accelerate as a result of activating the “fight or flight” instinct[2]. In opposite, blue colour has a calming effect.

However, not everyone can see colours. Approximately about 10% of human population has trouble seeing colours correctly. If you would like to deepen your knowledge about types of colour-blindness, please check the website. There you can learn about causes of colour-blindness, test yourself, and find a tool to check if prepared visualization is in line with best practices.

There are several basic principles that improve your colour palette and enable visualization for broader audience. To understand them we need to understand two important colour properties:  hue, and saturation. Hue defines colour in terms of pink, blue, yellow, or magenta. Saturation is nothing more than volume of the colour. By juggling these main properties we can improve or worsen results of our work.


First of all, stop using red-green palette which is confusing or even unrecognizable to colour-blinded people. This is my humble recommendation. For most people with colour difficulties this red and green colour look the same (see Picture 1).

Picture 1

Most modern data visualization tools, such as Tableau or Power BI already have available colour palettes that handle with the topic. Both mentioned tools have also option to create custom compositions and upload them to the application (custom colour palettes for Tableau and Power BI).

If you are wondering about the right colour palettes, check out the ones presented on Picture 2 and Picture 3. They are nice, clean, and fancy and will work for any reports.

Picture 2 – Vivid & Energetic
Picture 3 – Elegant & Sophisticated


Even though we try to avoid the red-green colour range there are still other pairs that resulted in similar way. In recent years I have been observing the dizzying career of the grey-blue duet. I like this combination as well, however, it is essential to match them wisely (see Picture 4).

Picture 4


Sometimes the best option is to simply stick with one colour and play with its saturation to differentiate specific categories or data ranges (see Picture 5). This approach can be used in most visualizations.

Picture 5

More practical colour ranges you can find here, and if you would like to test your composition on specific charts use this website.


Another interesting channel we can use to help visually impaired people easily distinguish between coded data is to assign shapes to different data categories. A good example of how the introduction of shapes can make difference is the well-known RAG.

RAG stands for RED-AMBER-GREEN and is widely used in business environment to communicate performances, risks or statuses of activities. It is most commonly used in project management to report status of tasks, but due to its simplicity, it is also used in data visualization to highlight for instance KPIs (key performance indicators) performance. Red indicates about underperforming, amber that something is an issue and needs to be monitored, and green that is fine.

But as you already know RED-GREEN can be very confusing for colour-blind people. So, my suggestion is to use a shape as another visual communication channel to make sure everyone is on the same page. Instead of format with coloured background, it would be better to introduce icons that have different shape and are coloured in red, amber, or green (see Picture 6).

Picture 6

But what about charts like line chart or bar chart? How can we improve distinction between specific lines or bars? We can use different patterns to distinguish one bar from the rest one or to present several lines on one chart (see Picture 7).

Picture 7


Written descriptions, recommendations or insights can be tricky. Especially when you want to use colour names to emphasise certain points, data categories or issues. How someone, who does not see green colour (see Picture 1) can understand a message “All departments represented by green bars have exceeded their sales targets this year”? This message must be rewritten to “Departments A,B, and C have exceeded their sales targets this year” to ensure that all stakeholders understand it.


In addition to the most recognizable challenge, which is colour blindness in data visualizations design, there is another related to vision loss due to age, accidents, or genetics. For those who suffers from low vision, we must remember that size and contrast of displayed text matters. Especially when we display some materials on screens in conference rooms, but even when you present something via communicators as Teams, or Zoom, size matters. You can read more about the topic here.


When it comes to the font size, there is no one good recommendation. It depends on the purpose. If you are going to display materials at a conference in a large conference room, it is better not to use smaller fonts than 18 when describing axes or legend and have less information on the slides. There is nothing wrong in having more readable slides rather than fewer but cluttered.

A different approach can be taken when creating reports. I would say use a font size 9 or 10 for axis or legend description, but in no other case should you go lower than 12. In reports crucial thing is to group information together or to display them in close proximity to make it easier to interpret or make decisions. That is why optimizing space is so important. These screens can always be enlarged, and anyone can take advantage of them.

Picture 8


The general rule is to maintain high contrast between background and foreground (e.g. white – black, black – white). A typical accessible barrier for people with low contrast sensitivity is grey text or figures on a light background. However, for some people better combination is with lower contrast, because they suffer from the bright background (e.g. they have to change a screen background to the darker to be able read what is on the screen).

As you can see there is no single best answer how to approach this challenge. A good practice is to give people the option to change the display mode from bright (light background and dark foreground) to dark one (dark background and light foreground).

Picture 9

By these small changes, we are bringing better user experience in our organizations or widely, if we prepare data visualizations for the media or other public usage.



A confusing tram trip in Cracow – How humans read information.

It was several years ago. I was in Cracow and, I made an appointment with my friends in a nice vegetarian restaurant. I took with me my nine-year-old daughter. To get there we took a tram. My daughter was very excited about the event and, as a typical child her age, the minute we entered the tram, she started asking where we were getting off.

Fortunately, we sat down just next to an information board, where all the tram stops were displayed. So, I told her stop’s name, pointed to the board, explained to her how it works and proposed counting the stops on her own. I didn’t pay too much attention to it because Cracow is my hometown, and I knew it wasn’t far.

What a surprise it was to hear: “Mom, we’re on the 12th stop”. Knowing it cannot be right (the right number was 3rd), I asked her to count them again, but the response was the same. This situation repeated a few times till eventually she exploded and yelled at me. I swiftly considered the hypothesis that she must have been swapped in the hospital (obviously my own child would be smart enough to correctly count to 5!) and rejected it. Finally, I looked at the information board, and everything became clear. 

The culprit of this confusion was interpretation of the information board with tram stops. You see, western civilization uses the left-to-right reading pattern, so this reading order seems natural to us[1]. Linguistic and reading patterns affect reasoning of time and space, as well as relations between these two dimensions. My daughter made a subconscious assumption that the tram stops on the board were displayed in the “normal” order. Her assumption was totally right.

However, it displayed stops according to tram moving direction (right to left) but not with alignment of left to right perception of time (unexpecting design choice). Even though it consisted of a direction arrow, names of stops, and a moving ball pointing to the current stop, my daughter’s brain was still searching for the familiar left-to-right pattern.

And that is why her answer was 12th (count from the left side the stop marked with yellow circle!, but the start of the trip is on the right side)

This story is a great example how people consume information embedded in the time and how they expect it to be displayed. It’s worth remembering that, in our culture, information is read from left to right and from top to bottom. When we work on reports, dashboards or any data visuals, the human brain uses built-in patterns, helping to store information and save energy. Following this simple rule significantly improves the user experience. 

Check out my other posts about importance of the time orientation in data visualization:


Circle Charts – when design meets data

  • Circle charts are better to use for entertainment or information purpose. They are not the best choice for a business environment.
  • Circle charts are attractive for receivers and can pull them into your story.
  • Using multilayers demands providing a well-defined legend.

Humans always have had a special attitude to the sun. In prehistoric and ancient ages, in some cultures sun had the status of God. Without any scientific theories, they just knew that the sun is unique and has a crucial role for our planet and any living creature. Even in cultures where ancient humans did not worship the sun, the sun motif was commonly used to decorating buildings, everyday items, or apparel.

Nowadays, we still willingly use the image of the sun, especially in art and architecture. Something is appealing in this figure. Centric circle shape with rays around them somehow reminds me of the wheel of life with rays as special moments.

Maybe that is why the pie chart and all variations of pie charts are so popular and like among people. The father of the most known data visualizations is William Playfair. He invented a pie chart in 1801, and it is still commonly used to depict data.

My personal relationship with a pie chart is …. complicated. I do not use them often in a business environment. It is hard to present accurate data on a pie chart, especially with a good number of categories. When it comes to present information for making decisions it is better to go for more readable visualizations like bar charts (check my post: “PIES ARE FOR EATING NOT FOR DISPLAYING DATA”).

However, a different story is with data journalism, when the purpose is to entertain, or inform the audience. In such case, I would give green light to anybody, who would like to present any complicated data on any variation of a circle chart like a sunburst, radial chart, or spiral chart.

Those charts give you an opportunity to present complex hierarchical information on one chart, so even though there are maybe not idealistically readable, they are still concentrated within one visualization, which is an advantage for the audience. Do not forget that data journalism has a different purpose. The main goal is to pull readers into the story. Surprisingly, more complex visualizations with a huge number of details, colors and shapes can be a better agent than simple one to achieve that mission. It is because readers must spend more time decoding that visualization and retrieve information from it. Another aspect that increases the involvement of readers is chart interactivity. Of course, that case can be applied only on website media.


Below infographics are good examples of the complexity vs. the reader engagement. It is hard to understand them at glance. You need to hang your eyes for a longer time and go deeper to acknowledge these images.

The huge advantage is adding other layers or rings to the image. Thanks to that technique additional data are introduced into a chart and we can interpret or read information from different angles or levels. Looking on the same image with several layers of information helps us to find interesting patterns and observation. Would be much harder to achieve that effect when having separate charts.

Global statistics

Our Mother Earth is round at it has a connotation with a round object like a circle. Why not use it to strengthen the message. The chart is combined with several charts placed on circle x-axis: life expectancy and average hours of sunshine is a bar chart. Life satisfaction is a heatmap.


The time in western culture is perceived as linear from years perspective. When we present years the line chart or bar chart would be our first choice. However, when it comes to the elements of one year, we perceive them as a cycle. What I definitely admire in circle charts is the possibility to present any periodical phenomenon connected with time:

  • Seasons: Summer, Autumn, Winter, Spring
  • Months
  • Weeks
  • Hours
  • Minutes

Hierarchical information

Presenting hierarchical data is challenging. However, sunburst charts can handle that. Sunburst charts consist of rings that represent a separate level of hierarchy. This visualization gives us an opportunity to present very complex information in one view.

Note that hierarchical information can be presented as qualitative or quantitative.

The below example presents types of cheese categorize by type of milk and their hardness. This information is qualitative. Another type of visualization that we could use would be a treemap. However, a treemap does not look such good as a circle chart.


  • Use colours to catch the attention but remember to choose them in accordance with best practices for colour blindness disabilities. Studies show that around 10% of people population have some disabilities in colours distinguish.
  • Always provide the legend. The legend should explain the meaning of colours, shape, sizes and even positions of objects on your visualization.
  • Add short text on visualisation. If there are points that should be emphasis place additional text with an explanation nearby them. The well-balanced text provides context for a particular point.
  • Plan the objects’ size with available space in mind and readability aspect.
  • Do not use too small fonts.
  • Do not use decorative fonts as they are not readable.
  • Remember about the title and short description of the data visualization.
  • Leave whitespace around the visualization to not clutter the page.