Designing maps for the colour-vision impaired

To design maps that are readable by the colour-vision impaired but are also appealing to those with normal colour vision successfully, cartographers need to know how the colour-vision impaired person perceives colour and which colour combinations become confused. In this article, we concentrate on red-green colour confusion, which is by far the most common form of colour-impaired vision, and suggest how maps can be designed to consider this user group. We also introduce Color Oracle (see http://colororacle.cartography.ch), a free application that allows the designer to see colours on the monitor as people with colour-impaired vision see them.