Visual clutter reduction in zoomable proportional point symbol maps

ABSTRACT

Proportional point symbols are commonly used in map displays. However, when such displays are zoomed out, the available map space shrinks and consequently symbols overlap and the display suffers from visual clutter. Therefore, solutions are needed to reduce visual clutter in zoomable map displays that contain proportional point symbols. The authors add to the body of knowledge through the investigation of the performance of three solutions: aggregation of unit areas, the displacement of overlapping symbols, and modified symbolization; four variations of modified symbolization are examined in detail. The original study begins with a consideration of the strengths and weaknesses of the solutions, with an emphasis on information loss. Thereafter, user sessions with 165 participants are arranged to gain empirical evidence of the performance of the solutions. The results reveal that although participants zoom out the map to zoom levels that implement visual clutter reduction techniques, they tend to zoom in the map and pan it to examine specific areas. Moreover, they willingly use the map with aggregated unit areas in cases when the solution facilitates task accomplishment. A certain amount of skepticism attaches to the solution that displaces overlapping symbols.

KEYWORDS:

• Empirical study
• proportional point symbol map
• user testing
• visual clutter

Acknowledgments

The web application used as the study material is a derivative of the software developed in the Department of Geography of the Norwegian University of Science and Technology as a deliverable of the ClimRes research project (see below).

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the project “Climate change, and natural hazards: The geography of community resilience in Norway” (ClimRes), funded by the Research Council of Norway’s KLIMAFORSK program [Grant number NRC 235490], and by the Polish National Science Centre [Grant number UMO-2016/23/B/HS6/03846], “Evaluation of cartographic presentation methods in the context of map perception and effectiveness of visual transmission.”