1. COLOR DISTANCE ON MAPS
Alžběta BRYCHTOVÁ
This presentation is co-financed by the
European Social Fund and the state
budget of the Czech Republic.

2. Introduction
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Color
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Color distance
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color hue and value - 2 of 6 Bertin‘s visual variables
in cartography there is a necessity to emphasize sufficient difference
of visual variables (Bjorke, 1996; Garlandini a Fabrikant, 2009; Harrie a Stigmar, 2009; …)
metric, that allows to quantify perceived difference between two
colors (CIE, 2012)
Demonstration:
Small color distance:

What is the sufficient color distance?
Big color distance:

3. Background
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Measurement of color distance:
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CIELAB perceptually uniform color space
Standard illuminant D65
CIEDE2000 formula (E00)
RGB color space vs.
CIELAB color space

4. Research task
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How is the influence of color distance on users ability to
read, compare and interpret visualized information
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choropleth maps
qualitative area feature maps
The hypothesis:
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increasing color distance will have positive impact on the map
users ability to compare two areas
increasing spatial distance between two areas will decrease
map users ability to compare them

5. Stimuli

6. Experimental stimuli
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quantitative color scales
6 categories (shades of green)
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qualitative color scales
6 categories (shades of rainbow)
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5 levels of color distance between adjacent categories
(E00= 2, 4, 6, 8 and 10)
3 levels of spatial distance between compared areas
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 330 stimuli to examine  only 106 stimuli selected
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7. Experiment
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web survey (LimeSurvey)
uncontrolled experimental conditions
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experiment structure:
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different devices, different color output
age, sex, color blindness, level of expertise
color vision test
106 stimuli
10 refreshing stimuli
monitored metrics:
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accuracy, time to answer

8. Experiment
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Participants:
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608 participants
250 evaluated responses
143 females (57.2%) and 107 males (42.8%)
20 to 70 years (20-30 years = 174 respondents ~ 69.6%)
the best time 16 min
the worst time 18 hours 

9. Experiment

Comments of participants:
Bětko, ty vrahu!
 It was too long!
 My eyes .... god dammit
 OMG! Crazy! The last 50% I was praying that it will with next
click and i will never see that terrible map again!
 Skoro mi vypadly oči z ďůlku :)
 it was sooo long:)) but I am patient:)
 Wow! So much clicking. Ideal for the evening before the exams
 …
participants in general lacked the assessment of their own
performance


10. Results
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problematic color distance

results based on the accuracy of answers
Choropleth maps
Qualitative maps
Less problematic E00=10, most problematic E00=2

11. Results

problematic color distance

results based on time to the correct answer
Choropleth maps
Qualitative maps
Most time consuming is E00=2, no other significant difference between groups of the same E00

12. Results

The influence of spatial distance of compared areas
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results based on the accuracy of answers
Choropleth maps
Qualitative maps
Most problematic is the biggest distance (fits with the hypothesis)
Higher incorrectness, no significant result based on the spatial distance

13. Results
 qualitative color scales with the same color distance between categories
are in general less readable, than choropleth color scales with the same color
distances
 „Humans are more sensitive on small change of color value than on small
change of hue“ (Voženílek & Kaňok, 2011)
 spatial distance has lower influence on qualitative color scales  humans
can better distinguish color shades based on their names (Brewer, 2003)

14. green
yellow
green
blue
green
orange
green
pink
green
green

15. Thank you for your attention…