Posted on: June 27, 2019 at 1:51 PM    

As spatial professionals, we put alot of effort into analysing data, visualising relationships and presenting outputs through beautiful maps. Web and mobile technologies have increased the exposure of geospatial technologies to more people in more locations. Amongst this rapid growth in physical access and exposure, we must always consider whether a wide range of users can actually make use of our maps: are they accessible?

Colour blindness affects many people. About 8% of males and 0.4% of females are impacted by one of many types of colour blindness. The prevalence of the condition makes it an important consideration for anyone in the spatial industry. The topic of web accessibility is gaining exposure globally, and has been for some time. Government-led initiatives include the setting and regulating of accessibility standards for public sector content, and in some cases this extends to the private sector. For interest, New Zealand’s public sector guidelines on web accessibility can be found here.

Below are some of the different aspects of colour related accessibility for mapping and some tools to assess and improve accessibility for colour blind users.

The colour blind cartographer

This is a unique situation, but not uncommon, where a cartographer might design a brilliant user-friendly map by their own perspective that does not communicate effectively to their non colour blind audience. In this instance, peer reviews and testing are vital to ensure that the final product serves its purpose. Cartographers with colour blindness should be aware of their impairment and its implications, there are many quick online ways to find out if you have colour perception issues, for example the EnChroma colour blind test:

The colour blind user

One of the more common graduated colour schemes used in displaying spatial information is the red to green colour ramp. The colour scheme is often effective as it fits a myriad of narratives, for example good to bad and low to high. However, the most common type of colour blindness also happens to be red-green deficiency.

Image1So how do we ensure that people with colour impaired sight can easily understand our visual content, whilst still delivering a clear message to the general audience?

For situations like the above green to red polyline symbology, we should probably first consider whether this colour scheme is necessary when communicating the underlying spatial information. If it is required, there are many situation-dependent adjustments that can be made to make the map more accessible. For example, we can try adjusting the hue of the colours in the colour scheme, adding labels from the display field, or adjusting symbol types.


There are many helpful tools out there that aim to enhance colour visualisations in all forms of media. For example, ColorBrewer is an effective and well-known tool for picking and testing colour gradients. Users can apply ramps of three to ten graduations and review them on a generic map. There are options to filter the pre-generated colour ramps by colour blind friendly, print and photocopy friendly. Some GIS products have built-in visual filters to show the perspective of various colour blind users, making it easier to measure this sort of accessibility at the desktop level. Esri have invested in developing colour gradients that are more accessible to colour blind audiences – these are prevalent in ArcGIS Pro. A number of extensions are also available for the Chrome browser to assist with colour blind accessibility, as follows:

Color Enhancer

This extension can be recommended to users with colour impairment. Users can visually define settings within the extension and enable a filter that best adjusts colour on the browser window to suit their impairment.


This extension sits within the DevTools menu of Chrome. It allows map makers and developers to quickly assess their web pages and maps for various types of colour blindness.


There are many examples of cartographic outputs that do not cater to people with colour blindness. Tools like the above can easily become a staple for spatial developers and web cartographers. Consideration of how our spatial content will be received by a wide range of audiences has always been a critical aspect of cartography, and these tools make it a much easier task when creating content that is accessible for everyone.

The design and adjustment of map elements can become a very tedious task. However, when catering for the colour blind audience there are often really simple things we can do that will drastically enhance map readability for them. It is a team effort for our industry to ensure our maps are more accessible to the colour blind audience.

Blog written by Steve Ford, Spatial Analyst & Developer








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