Data Visualisation: Principles and practice

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Henry Partridge GM Analyst Network Data Visualisation: Principles and practice Data Lab Manager 17 May 2018

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Trafford Data Lab https://www.traﬀorddatalab.io/

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• Clarity • Openness • Reproducibility Principles

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Clarity

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We strive for an economy of style in all of our data visualisations.

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“Chart time! It's ﬁrst Q shipping it garnered 19% market share, Palm 9.8%, RIM 39%, other 20%, Nokia 7% …" Macworld 2008 keynote Source: Macworld 2008 keynote; www.engadget.com

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Cleveland’s perceptual hierarchy 1 Position along a common scale Scatter plots 2 Positions along non-aligned, identical scales Small multiples 3 Length, direction, angle Waterfall chart 4 Area Treemap 5 Volume, curvature 3D bar charts 6 Shading, colour saturation Continuous color scale Source: Cleveland and McGill (1984) Accuracy

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Pie chart vs bar chart Source: Cleveland and McGill (1984: 533)

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“A table is nearly always better than a dumb pie chart; the only worse design than a pie chart is several of them, for then the viewer is asked to compare quantities located in spatial disarray both within and between charts […] Given their low density and failure to order numbers along a visual dimension, pie charts should never be used.” — Edward Tufte (1983)

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Tufte’s aesthetic guidelines

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Tufte’s aesthetic guidelines

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Wilkinson’s Grammar of Graphics Source: Wilkinson (2005) "A statistical graphic is a mapping from data to aesthetic attributes (colour, shape, size) of geometric objects (points, lines, bars)." — Hadley Wickham (2016)

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Rosling’s bubble charts Source: gapminder.org Variable Geometry Aesthetic GDP per capita ($) point x-position Life Expectancy point y-position Population point size Continent point ﬁll

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Rosling’s bubble charts in ggplot2 Source: gapminder.org

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Lab visualisation style https://traﬀordDataLab.io/assets/theme/ggplot2/theme_lab.R

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Lab visualisation style https://www.traﬀorddatalab.io/info/community_safety/burglary/index

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Openness

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We are committed to the sourcing, preparation and publication of open data.

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5-star Open Data Source: http://5stardata.info/en/

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Deﬁbrillators Source: https://www.traﬀorddatalab.io/maps/explore/

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Open data portal Source: https://www.traﬀorddatalab.io/data

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Reproducibility

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We will publish the data and code that drive our data visualisations.

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Example visualisation https://www.traﬀorddatalab.io/info/demographics/languages/R/ﬁg1.R

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Data Source: https://www.traﬀorddatalab.io/info/demographics/languages

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Image Source: https://www.traﬀorddatalab.io/info/demographics/languages

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R code Source: https://www.traﬀorddatalab.io/info/demographics/languages

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R and (RStudio)

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• Re-run code or adapt with diﬀerent data • R is a language so it is readable as text • Post R code via Twitter, reddit, email etc Reproducibility in R