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Course notes

Modified

May 28, 2026

Annotating charts
There are two distinct strategies for placing text on a chart:

Stylized text describing tidy data principles.

Data wrangling (I)
We’ll use the penguins dataset throughout this lesson to demonstrate {dplyr} operations. If you need a reminder of its structure:
 
Data wrangling (II)
Data for real projects rarely lives in a single table. A hospital database might have separate tables for patients, visits, diagnoses, and prescriptions. A course system…

Deep dive: coordinates + facets
A coordinate system combines the x and y position aesthetics to produce a two-dimensional location on the plot. It also determines how axes and panel backgrounds are drawn.…

Deep dive: layers
Throughout this lesson we’ll use data on houses sold in Tompkins County, NY from 2022–24, scraped from Redfin.

Deep dive: stats + scales + guides
The World Bank publishes a rich and detailed set of socioeconomic indicators spanning several decades and dozens of topics. Here we focus on a few key indicators for the…

Deep dive: themes
A theme is a collection of visual settings that control every non-data element of a plot: text sizes and fonts, background colors, grid line weights, legend positions, axis…

First instance of the chart. Originally published in The Economist

Implementing accessibility
In early 2020, “flatten the curve” became one of the most widely shared data visualizations in history.

A qualitative color palette showing distinct hues for unordered categories.

Optimizing color spaces
Color in data visualization serves distinct purposes. Using color that matches its intended purpose makes charts easier to read; mismatched color usage introduces confusion.

A Fox News chart showing top tax rates with a truncated $y$-axis that exaggerates the difference.

Qualities of great visualizations
In his book The Truthful Art, Alberto Cairo argues that a great visualization must satisfy five interconnected qualities:

The grammar of graphics
The grammar of graphics is a formal framework for describing statistical visualizations, originated by Leland Wilkinson in 20011 and extended by Hadley Wickham in his…

John Snow's 1854 map of cholera deaths in London's Soho district, showing death locations as black bars and water pump locations as dots. Deaths cluster tightly around the Broad Street pump.

Visualizing spatial data (I)
Data visualization and cartography have been intertwined since at least 1854, when Dr. John Snow mapped cholera deaths in London’s Soho district:

Diagram showing the seven simple feature geometry types: Point, Linestring, Polygon, Multipoint, Multilinestring, Multipolygon, and Geometry Collection.

Visualizing spatial data II
Raster maps provide a photographic background but give no access to the underlying geography. For complete control over the geographic elements of your geospatial…

Source: YouGov

Visualizing survey data
A poll is a survey or inquiry into public opinion conducted by interviewing a random sample of people.
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