alžběta brychtová - color distance on choropleth maps

This presentation is co-financed by the European Social Fund and the state budget of the Czech Republic.

COLOR DISTANCE ON MAPS

Alžběta BRYCHTOVÁ

Introduction

Color 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; …)

Color distance metric, that allows to quantify perceived difference between two colors

(CIE, 2012) Demonstration:

What is the sufficient color distance?

Small color distance: Big color distance:

Background

Measurement of color distance: CIELAB perceptually uniform color space Standard illuminant D65 CIEDE2000 formula (E00)

RGB color space vs. CIELAB color space

Research task

How is the influence of color distance on users ability to read, compare and interpret visualized information choropleth maps qualitative area feature maps

The hypothesis: 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

Stimuli

Experimental stimuli

quantitative color scales 6 categories (shades of green)

qualitative color scales 6 categories (shades of rainbow)

5 levels of color distance between adjacent categories (E00= 2, 4, 6, 8 and 10) 3 levels of spatial distance between compared areas 330 stimuli to examine only 106 stimuli selected

Experiment

web survey (LimeSurvey) uncontrolled experimental conditions

different devices, different color output experiment structure:

age, sex, color blindness, level of expertise color vision test 106 stimuli 10 refreshing stimuli

monitored metrics: accuracy, time to answer

Experiment

Participants: 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

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

Results

problematic color distance results based on the accuracy of answers

Qualitative maps

Choropleth maps

Less problematic E00=10, most problematic E00=2

Results

problematic color distance results based on time to the correct answer

Most time consuming is E00=2, no other significant difference between groups of the same E00

Qualitative mapsChoropleth maps

Results

The influence of spatial distance of compared areas results based on the accuracy of answers

Qualitative maps

Choropleth maps

Most problematic is the biggest distance (fits with the hypothesis)

Higher incorrectness, no significant result based on the spatial distance

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)

green

green

green

green

green

blue

yellow

pink

orangegreen

Thank you for your attention…