Thursday, June 27, 2019

Maps Will Tear Us Apart (Again)

Peter Saville's cover for Joy Division's Unknown Pleasure album has become an iconic image. The album cover was inspired by a visualization of the radio waves emitted by a pulsar, which was published in the Cambridge Encyclopaedia of Astronomy. In data science a visualization which is inspired by the graph is often called a 'joyplot' in acknowledgement of the iconic album cover. Although there are probably just as many data scientists who hate the term and refer to these type of visualizations as 'ridgeline plots'.

Over the years a number of maps have used rideline plots, often to signify population density. For example Giorgi Kankia's Population Lines uses ridge-lines to show population density in the country of Georgia. On his map the height of the ridge-lines relate to the number of people living within a square kilometer. The areas shaded red are Russian occupied areas of the country.

James Chesire was perhaps the first person to use a ridgeline plot to map population density (although James himself says this form of map visualization isn't entirely new). His Population Lines map uses ridge-lines to show population along lines of latitude using data from NASA's Sedac. James' population density map has inspired many other population density maps. For example, here is Henrik Lindberg's joyplot map of European population density.

Ridge-lines plots can also be used to visualize elevation. Kenneth Field has published a tutorial on how you can create a ridgeline plot map from a digital elevation model in ArcGIS Pro. His Joy Plots in ArcGIS Pro also includes a brief history of joy-plots. You can enjoy an interactive joy-plot elevation map at San Francisco Terrain.

Joy-plot maps have also been used to visualize Global Temperature Change and the Population of Wisconsin.

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