Cartogram Visualization for Bivariate Geo-Statistical Data

Abstract

We describe bivariate cartograms, a technique specifically designed to allow for the simultaneous comparison of two geo-statistical variables. Traditional cartograms are designed to show only a single statistical variable, but in practice, it is often useful to show two variables (e.g., the total sales for two competing companies) simultaneously. We illustrate bivariate cartograms using Dorling-style cartograms, yet the technique is simple and generalizable to other cartogram types, such as contiguous cartograms, rectangular cartograms, and non-contiguous cartograms. An interactive feature makes it possible to switch between bivariate cartograms, and the traditional (monovariate) cartograms. Bivariate cartograms make it easy to find more geographic patterns and outliers in a pre-attentive way than previous approaches, as shown in Fig. 2 . They are most effective for showing two variables from the same domain (e.g., population in two different years, sales for two different companies), although they can also be used for variables from different domains (e.g., population and income). We also describe a small-scale evaluation of the proposed techniques that indicates bivariate cartograms are especially effective for finding geo-statistical patterns, trends and outliers.

A Comparison of Visualizations for Identifying Correlation over Space and Time

“…Bivariate cartograms [66] use color or shade to encode a second variable in addition to that mapped to size. A recent variation on bivariate cartograms was presented by Nusrat et al [45], in which two variables are visually encoded with size.…”

“…For identifying moving patterns, Griffin et al [21] show that animation leads to better results than small multiples. Other studies that consider temporal change focus on comparing only two points in time (e.g., [44,45]). They do not provide insights about the compared techniques' performance for identifying trends over space and time.…”

“…Others have looked at two variables on a map (bivariate maps), but at a specific point in time [15,18,45]; or at how to visualize the correlation between two variables [31,52,53,69], including visualizations that can be used to depict temporal evolution [26], but not in a geospatial context. To our knowledge, how effective visualization techniques are at communicating correlation between two thematic variables, that evolve over both space and time, remains to be studied.…”

Multivariate Maps—A Glyph-Placement Algorithm to Support Multivariate Geospatial Visualization

“…They use a juxtaposed view to present equal area cartograms for different variants. Nusrat et al produce a cartogram that presents bi-variate data using a ring encoding, where the color presents the leading statistic, and the ring thickness presents the value the leading statistic [26]. This differs from our work by emphasizing bivariate design, whilst we provide options for up to nine dimensions to be represented clearly.…”

Flood Evacuation Mapping Using a Time–Distance cartogram

“…Cartograms have become popular in various fields of application to supplement existing maps [13,14]. They take an advantage of visualizing geographical information with statistical information simultaneously [15]. Although a cartogram might distort the actual geometry of the map, it is more helpful in understanding the intended attribute of the phenomena.…”