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Archived Comments for: Is NHS dentistry in crisis? 'Traffic light' maps of dentists distribution in England and Wales

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  1. Red - Green Colourblindness

    Chris Ballentine, University of Manchester

    10 May 2004

    I followed with interest the BBC web news about your paper and the distribution of dentists in the UK. I was disappointed on following the link to your 'traffic light' map that this uses a red-green extreme colour key. Like me, a significant % of your audience will be red-green colour blind. The use of the 'traffic light' analogy for a simple public message is great, but there are many other colour schemes that will not result in 10% of them seeing red (or is it green?)!

    Competing interests

    None declared

  2. Red-Green Color Blindness and Map Design

    Francis Boscoe, NYS Department of Health

    24 May 2004

    In addition to red and green, there are a variety of color pairs that tend to be difficult to distinguish by those with so-called 'red-green color blindness', such as orange and yellow. Fortunately, cartographers have thoroughly researched this problem and have designed a variety of color schemes that are discernable by nearly all with color-vision impairments (1). Examples of these color schemes are freely available at (2). The 'traffic-light' color scheme is fine so long as bluish-green is used in place of green.

    (1) Olson JM, Brewer CA. An evaluation of color selections to accommodate map users with color-vision impairments. Annals of the Association of American Geographers 1997; 87: 103-134.

    (2) Harrower M, Brewer CA. an online tool for selecting colour schemes for maps. Cartographic Journal 2003; 40: 27-37.

    Competing interests