The effect of spatial distance on the discriminability of colors in maps

ABSTRACT

The spatial distance (gap) between map symbols can have a great impact on their discriminability, however, there is little empirical evidence to establish spatial and attribute thresholds. In this paper, we examine the effect of the spatial gap in discriminability of color hue and value, that is, we conducted an online study to obtain performance metrics; then an eye-tracking study to understand participants’ strategies and cognitive processes. Participants completed two experimental tasks (compare two areas and decide if their color is the same; and compare three areas and rank them from the lightest to the darkest). The color distances and the spatial distances were strictly controlled for the compared areas. Our analyses confirmed that, overall, increasing the gap between colors has a consistent negative impact on the ability to differentiate them with both sequential and qualitative schemes. Furthermore, we observed that sequential schemes require larger color distances than qualitative schemes for discriminability. Finally, our results suggested that for qualitative colors, the largest tested color distance ∆E₀₀ = 10 yields considerably higher levels of accuracy in color discrimination (even when the spatial gap between the two colors is large), thus we recommend ∆E₀₀ = 10 to practicing cartographers and other information visualization designers.

KEYWORDS:

• cartography
• color schemes
• spatial distance
• color distance
• usability
• eye-tracking

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. We differentiate between varying confidence levels of 0.01 and 0.05 with a notation of a two asterisks (**) and single asterisk (*) respectively. This notation will be used throughout the paper.

2. A < B < C means that A is lighter than B and B is lighter than C; A = B means color shades are identical.

Additional information

Funding

This work was supported by the ESF under Grant [grant number StatGIS CZ.1.07/2.3.00/20.0170].