Evaluating Cartogram Effectiveness

Abstract

Cartograms are maps in which areas of geographic regions, such as countries and states, appear in proportion to some variable of interest, such as population or income. Cartograms are popular visualizations for geo-referenced data that have been used for over a century to illustrate patterns and trends in the world around us. Despite the popularity of cartograms, and the large number of cartogram types, there are few studies evaluating the effectiveness of cartograms in conveying information. Based on a recent task taxonomy for cartograms, we evaluate four major types of cartograms: contiguous, non-contiguous, rectangular, and Dorling cartograms. We first evaluate the effectiveness of these cartogram types by quantitative performance analysis (time and error). Second, we collect qualitative data with an attitude study and by analyzing subjective preferences. Third, we compare the quantitative and qualitative results with the results of a metrics-based cartogram evaluation. Fourth, we analyze the results of our study in the context of cartography, geography, visual perception, and demography. Finally, we consider implications for design and possible improvements.

The State of the Art in Cartograms

“…Until recently, little Work was done on analyzing the effectiveness of different cartograms, beyond some ad hoc performance analysis, typically comparing a new method against an existing one, using metrics such as cartographic error and running time. In the last decade more Work has been done on evaluating cartogram algorithms, both by a standard set of performance measures and by subjective preference and user‐studies [AKV15, KFF11, NAK15]. Finally, cartograms are more frequently used as off‐the‐shelf tools, in social, political and public health applications.…”

“…A recent study [NAK15] evaluated four major types of cartograms (contiguous, non‐contiguous, rectangular, and Dorling), based on the task taxonomy for cartograms. The results of this study show significant differences in performance (in terms of task completion time and accuracy) between the four types of cartograms.…”

“…Nusrat et al [NAK15] also used subjective preferences, after performing several tasks, to evaluate four types of cartograms (contiguous, non‐contiguous, rectangular, and Dorling). To understand user preferences about different aspects of cartograms, the semantic differential technique of Dent [Den75] was used.…”

Feminist cartography and the United Nations Sustainable Development Goal on gender equality: Emotional responses to three thematic maps

“…A contiguous cartogram deforms map regions because the original polygons are pulled, pushed, and stretched (Nusrat et al ), but maintains adjacencies and statistical, topological, and geographical accuracy better than other types of cartograms (Nusrat and Kobourov ). Cartograms may be a more socially just form of mapping because they provide a more equitable representation of the world (Dorling ).…”

go-cart.io: a web application for generating contiguous cartograms

“…This status quo has been against the current trend towards "citizen cartography", mainly driven by online tools that enable even untrained users to produce maps from their own data. It has been shown that most users perceive contiguous cartograms, though potentially challenging to read, as an effective method to display data [9]. It is therefore timely to develop a new web interface that makes it easier to generate cartograms.…”