In Lesson 1, Topic 2 we reminded ourselves about the different scale types that our data variables can fall into (nominal, ordinal, interval, ration). In this 3rd topic of Lesson 1, we’ll consider how people use these variables to create graphical displays that can show us what the data contains. Instead of just jumping right into consideration of common chart types, we’ll first consider the basic building blocks of all charts: marks and channels. In the next topic, we’ll cover the first of two criteria of evaluation: expressiveness of encodings.
Munzner’s diagram showing different types of marks
Munzner’s diagram showing different types of visual channels
Exercise 1.3. Take a look at the chart below – a chart called a Treemap that we’ll cover in Lesson 4 – and see if you can identify the mark type used in the chart as well as the encoding channel used for the Population variable:
Mark type (points, circles, squares or rectangles):
Encoding channel for Population (position, area, volume, tilt, or color):
“A visualization represents data using a collection of graphical marks such as bars, lines, and point symbols. The attributes of a mark — such as its position, shape, size, or color — serve as channels in which we can encode underlying data values. With a basic framework of data types, marks, and encoding channels, we can concisely create a wide variety of visualizations.”
Jeffrey Heer