Geography Reference
In-Depth Information
Use yellow with care and avoid yellow-green colours altogether in spectral
schemes; and
Use colour intensity to reinforce hue as a visual indicator of magnitude.
Light and Bartlein (
2004
) also proposed solutions for representing diverging and
sequential colour schemes. Diverging data should be represented by using two
complimentary colour schemes that diverge from a common hue. Here, colour
intensity can indicate magnitude and hue can indicate sign (increase or decrease).
Sequential data can be shown with colour schemes that use a sequence of lightness
steps combined with a single hue or with a hue transition.
Distinguishing point classes is a problem for the colour-blind. As many thematic
maps use dot symbols for representing information strategies need to be put into
place for producing legible graphics. Research by Jenny and Kelso (
2007
) deter-
mined that by varying saturation, contrast can be increased, which improves
interpretation by red-green impaired users. They also found that shifting hue from
green to blue improves legibility. The optimum design was achieved by
distinguishing between geometric shapes by varying hue and saturation. They
also made comments about their success when colour was discarded altogether
and differences in mapped data shown by different shaped symbols.
Jenny and Kelso (
2007
) also determined that line classes can be better differen-
tiated for the colour-blind if colour specifications were also amended in a similar
way as for dot symbols. Additionally varying line width also improved compre-
hension, and line annotations were also found to be beneficial, as well as removing
the need to have a legend.
Distinguishing area classes is also a problem for colour-blind map readers.
Different hues can be employed, as long as each hue has a unique saturation (the
density of colour applied) and value (intensity). The addition of hachuring can also
assist to improve legibility.
In some instances colour visualizations are designed so that one colour merges
into another. Here, to improve legibility Brewer (
1997
) suggests the following
design strategies:
Vary lightness on the red-orange-yellow end of the rainbow;
Omit yellow-green to avoid confusion with orange; and
For bipolar data, omit green and use a scheme with red, orange, yellow, light
blue and dark blue; and align the yellow-blue transition-diverging data range.
The needs of the visually impaired and blind for Web access and interface design
are being addressed by the World Wide Web Consortium
s accessibility initiative
'
(W3C
2000
) that includes
from graphics into audio for the blind.
A number of mapping organisations have addressed colour-blindness and map
design specifications. For example,
translations
'
'
s Ordnance Survey
re-designed their topographic maps to ensure that they are readable by the colour-
blind (The Map Room
2009
; Ordnance Survey
2009
). Digital mapping from the
Ordnance Survey can now be customized to create
the United Kingdom
'
colour-blind-friendly styles
.
'
'
