Data visualisation and colour blindness


John Dodsworth is a director of Beacon Dodsworth and has worked with geographical information systems since the early 1990s. Those of us who work with him know that he is colour blind, a fact that those who have used the GIS systems and maps he has created might be surprised to hear. With the current prevalence of infographics and data maps daubed in red informing us about the risks of coronavirus, John wanted to write about his experience of colour blindness in a world of colourful data, charts and maps.

I am colour blind (CB). There are several types of colour blindness. Mine is a common one that I call red-green colour blind because the technical terms, deutan colour blindness, deuteranopia, or Daltonism, don’t convey it any better. I am not blind (just not very observant) and I do see colour (monochromatic visual impairment is extremely rare). About 8% of males are CB. 

It is an interesting condition: I find it not so bad to be life-limiting, but for many people there are daily frustrations and obstacles that could easily be helped by awareness and easily and cheaply implemented techniques. As a CB person you never know what you are missing (despite being told by well-sighted, and hopefully well-meaning, people). One advantage it does give is a tiny insight to the world of someone who does have a life-limiting condition.

Colour blindness and a career in mapping


Whilst not life-limiting, there are several professions barred for CBs, often for good reason. For example, when I was young I wanted to be an electronics engineer but being unable to distinguish the colour bands on resistors quickly suggested that I should get my kicks elsewhere; that has probably contributed hugely to national safety.

I can’t claim that data mapping is the perfect industry for someone with colour blindness either; especially with people’s natural propensity to use red-amber-green as a default colour choice on many kinds of map. But it has given me a useful take on displaying maps that are accessible, and understandable, to all audiences.

Changing perceptions of colour blindness?


I didn’t know until my teens that I was CB. At school I was criticised for drawing purple skies and brown grass with crayons so I quickly learned to use only crayons that still had the paper wrapper with the colour name on. You see, we know that grass “is” green and sky “is” blue in the same way that anyone does. I also recall joining in with the “aren’t the autumn colours wonderful?” chorus while secretly wondering what all the fuss was about. I love autumn for quite different reasons.

My older sister at secondary school even did a school science presentation on colour blindness and used me as an object lesson. By that time I had come across the Ishihara test and I wonder how many others have been equally delighted to see either nothing or the “wrong” numbers on those splashes of coloured dots. Simple testing still isn’t as widespread as it should be.

Unfortunately I can’t say that attitudes have really changed much over the years. A recent visit for new glasses surprised me when, well into the eye test, the optician asked “which is clearer, red or green?” and when I told him I couldn’t distinguish them, sighed and simply moved on to the next test.

Presenting visual data to the colour blind


Colour Blindness, like any deficiency, causes one to seek other cues and clues in a wider range of factors such as context, pattern or texture. I’ve learnt that colour alone, no matter how striking it may seem to you, isn’t enough to convey meaning to every audience. The coronavirus pandemic has really brought this to the front of my mind as every agency, outlet, and influencer bombards us with charts and maps to try and help us make sense of these strange days.

Charts with lots of different-coloured wiggly lines tell us when we can expect to die. CB folk can’t work out what their chances are because so many of the lines are similar colours. The key (legend) is rendered useless unless the lines themselves are labelled in some other way or very contrasting colours are used. Even block colour can be a problem.

Colour blindness and mapping


What’s true of charts is also true of maps. Since a large part of Beacon Dodsworth’s business is making software that makes maps, we are keenly aware of the need to display at-a-glance information in such a way that it won’t confuse or mislead the audience. We delegate the responsibility for colour and labelling to our users but we have a part to play in offering palettes and colourways that encourage clarity for all users.

Maps are better than charts in this respect because the colouring often involves large areas, which are easier to discern and separate. The good news is that maps have lots of other attributes that help you to show/hide your message/the truth: projection, scale, resolution, etc. A large area filled in a pale pastel colour can be made less significant than a vivid neighbouring smaller area. Of course, we would prefer it if mappers used different fill styles (symbols or cross-hatching) to make visual distinction less reliant on colour.

Avoid the traditional RAG (Red-Amber-Green) colour scheme in your maps, even (especially) if you are mapping life or death statistics. Red-green colour blindness is the most common type and, even without colour blindness, the human eye finds it particularly difficult to differentiate shades of red. Ideally, use a unique colour, rather than shade, for each data variance accompanied by other visual cues such as pattern.

If you are limited to a handful of colours, then consider that the human eye is better able to differentiate blues and greens – and they often look less bleak than shading large areas of the population in blood red. For example, if you are creating a choropleth or “heat” map, rather than using a traditional red, amber, green colour range, make a more literal “heat map” and grade your results from a cold blue up to a fiery red.

Short of full colour blindness, sufferers tend to struggle with complementary colours: either on the red-green or yellow-blue spectrum. It follows that if you avoid working with a complementary colour scheme you have a better chance of making the data on your map clear to the most viewers. The artists in the audience might cringe but, as a data mapper, creating maps that are easy to understand at-a-glance is far more important than creating a delicately shaded thing of beauty. However, although this works for me, I must emphasise that this will not work for everyone with CB, so always ensure you never rely on colour alone to differentiate your data.

Once you have drafted your map with a thoughtful colour scheme and alternative signifiers such as patterns and data labels you should also check your work for accessibility. People experience CB in different ways and so even I can't hope to provide a fair evaluation of a visual's overall accessibility. Whether a colour scale works for everyone or not depends upon the specific shades of colours used and the colour contrast ratios between them so it is difficult to make general rules. Fortunately, Google have introduced a Colour Blindness rendering option into Chrome - tucked in their developer tools - to simulate how we see the world. If you are working with an online mapping tool like MapVision, you can check your workings before sharing your map with a wider audience. There are also organisations out there dedicated to helping you make your work as accessible as possible, one of the more prominent is Colour Blind Awareness who are very active on Twitter.

A colour key for electrical resistors showing how the colours can be difficult to differentiate.

Dodsworth Electricals: no refunds. Even a cursory glance at a resistance colour code chart shows the easy confusion between brown and red, blue and violet, orange and gold.

An example of an Ishihara test image.

An example of an Ishihara plate, the most well known colour blindness test, created more than 100 years ago and still in use today. If you see the Mona Lisa here you have other problems.

 

A selection of infographics that rely too much on colour, especially the red spectrum.

Don't rely on colour alone. Although these infographics use contrasting colours, matching the data with the key is difficult because of the small areas in the key.

A traditional red to green choropleth map.

A traditional choropleth map with a red to green colour range. This is what people often default to when making a map but not at all friendly to someone who is colour blind as Google's deuteranopia emulator shows below:

A traditional choropleth viewed using Google's deuteranopia emulator

A choropleth map themed in MapVision to be more accessible to Colour Blind users.

The same map made to be more accessible in MapVision, our online mapping system. It avoids complementary colours, has a large key, and uses patterns to avoid reliance on colour alone. This version retains far more clarity when seen using Google's red-green colour blindness emulator:

A choropleth designed to work for users with red-green colour blindness seen through a deuteranopia emulator.

We've spent more than 25 years visualising complex data and making it easy to understand.
If you'd like to see if we can help you please get in touch.

online or call us on:

Our other blogs

How far is it to the beach

We use Beacon Dodsworth's scripting technology to answer that most important of questions when the sun finally does threaten an appearance.

Cycle to work day

Each year for #cycletoworkday we take a look at cycling statistics across the country and try to map that data and find interesting trends. This is mainly because we at Beacon Dodsworth are either a little bit obsessed about cycling, or we tend to worry about the environment.

Postcode to postcode drive time and distance

What happens if we want a postcode to postcode drive time lookup table?

The new normal for the GIS world

Toby, our Account Manager, looks at the changes to working style and client needs in the geodata industry following the COVID-19 outbreak.

Geodemographics and the University of East London

The University of East London explain how they have been using our P² People & Places geodemographic classification.

How to back up your Prospex data

Keep your GIS projects safe by using the in-built Prospex back up process. Here is how.

What is geodemographic profiling?

More than 64 million people live in the UK, each with their own outlook, priorities, needs and way of life. Geodemographic profiling offers a way to group these individuals to try and identify the right audience for your product or service.

Data visualisation and colour blindness

John, our director talks about living and working with colour blindness in the mapping industry where colours are pivotal in adding dimensions to people's understanding.

What has the census ever done for us?

How Census 2011 can be used to help organisations with demographic analysis.

All you need to know about postcodes but were afraid to ask

The humble postcode has been around for years. We look at how postcodes are used and what led to their introduction.

Who spends most on Fruit and Veg

National Vegetarian Week (#NationalVegetarianWeek) this year runs from 11th to 17th May. What better opportunity to highlight how GIS mapping can be used to create marketing campaigns and raise awareness of the benefits of eating more fruit and veg.

Google Fusion Tables

After almost 10 years of service, Google retired their Fusion Tables product at the end of 2019. This tool was very useful at visualising and sharing large amounts of tabular data - particularly amongst small and mid-sized businesses. So what can we do to fill the gap left by this tool?

Yorkshire Day

As a Yorkshire-based company, we wanted to help celebrate Yorkshire Day, which takes place on 1st August. Naturally, we wanted to put a geographic spin on the celebration, so we took a look at drinking preferences within God’s own county.

Mapping GP prescription data

An article by Allan Brimicombe (Head of Centre for Geo-Information Studies at the University of East London) & Pat Mungroo on using GP prescription data to understand health needs.

Administrative Geography

Administrative geography is a way of dividing the country into smaller sub-divisions or areas that correspond with the area of responsibility of local authorities and government bodies. It provides an alternative to postcode geography but because it tends not to be used by consumers, it is often overlooked. We take a look at administrative geography, what it is and how to use it.

Mapping for local projects

Recently, we were contacted by a company responsible for organising charity door knockers. They needed more than 9,000 postcode sectors mapped at A4 size to pass to ground staff showing street level detail. This would enable them to use maps at a local level to plan fundraising routes and clearly define territories for each agent.

The foundations of geographical analysis

Displaying data on maps makes it easier to understand as well as giving a new perspective on a problem. Using a GIS to prepare and present data has become increasingly popular over the last 20 years, but graphical displays of data on maps were around long before computers came along.

Social change over 10 years

The next census isn’t due to take place until 2021 so we thought it was a good time to take stock of some of the changes and trends we noticed between the 2001 and the 2011 census. What difference does 10 years make to our society and the people that live within it?

Using geographic intelligence to grow the UK’s broadband network

Using geographic intelligence to sustainably grow the UK’s broadband network.

The power of postcode sectors

Postcode sectors are aggregations of individual postcodes and they provide meaningful geographical reporting areas in any GIS. However, they aren't as easy to map as you might think. Here is how we do it.

Living Costs and Food Survey

The Living Costs and Food survey (LCF) is compiled every year and is used by the UK and European governments, Department for Transport (DfT), and Her Majesty’s Revenue and the Customs (HMRC). But what is it, and why should we care?

Where is the North

We've used the territory manager tool in Prospex GIS to split the UK into north, south and east and west with equal population counts.

What is GIS software?

A Geographical Information System (GIS), is a tool for analysing, visualising, managing and presenting data that is related to a physical, geographical location. That link to geography is the key difference between GIS and other data visualisation techniques.

Get in touch
Call  01904 701020, complete   or