Wednesday, 19 August 2020

Radar and Venn diagrams

Using a radar diagram

Line charts in circles, 1874

Brief History

Initially, a radar diagram was used by Georg von Mayr (Germany, 1841-1925) in the Journal of Royal Bavarian Statistical Bureau 1874 and the name of the chart was line charts in circles. Other current names are radar, spider or web chart.

Common Context

In a data set with two or more numeric characteristics, the radar chart offers a visual representation of the numeric value of each characteristic. The possible values of a characteristic are scaled on a radius of the radar. Therefore, the radar will have the same number of radii as the number of characteristics studied in the data set. The clockwise order of characteristics in the radar is the same for each data element, otherwise, the visual diagram will confuse the reader. 

In the below graph, a coffee taste rating is compound from rating aroma, flavour, aftertaste, acidity, body, and balance. The selected element is a coffee from Peru, with Aroma rating 8.42, Flavour rating 8.5, Aftertaste rating 8.33, Acidity rating 8.5, Body rating 8.25, Balance rating 8.25.

Coffee Ratings with Radar and Venn Diagrams


About Venn Diagram

Eulerian Circles, 1880

Brief History

The above image is a fragment from the article "Diagrammatic and Mechanical Representation of Propositions and Reasonings" 1880, where John Venn (England, 1834-1923), described Eulerian Circles, initial name given to a Venn diagram. Other current names are set diagram or logic diagram.

Common Context

A Venn diagram is helpful to represent the relationship between sets of data, by comparing the differences and similarities of data sets. A data set is drawn as a circle. In the intersection of the circles, there are the elements found in all the circles where the intersection belongs to. The elements particular to a circle are in the area of the circle that is not in the intersection. Usually, the size of the circle is proportional with the size of the data set or group. 

In the above "Coffee Ratings" figure, all the countries are next to each other in the intersection of all circles - the four countries have almost equal values for each characteristic.

References

Radar Chart, History of Infographics by RJ Andrews, history.infowetrust.com/#mayr1

The radar chart and its caveats by Yan Holtz, data-to-viz.com/caveat/spider.html

Coffee ratings Tidy Tuesday Challenge by R4DS Online Learning Community,   https://github.com/rfordatascience/tidytuesday/blob/master/data/2020/2020-07-07/readme.md

Venn Diagram, History of Infographics by RJ Andrews, history.infowetrust.com/#venn1

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