7.2 Visualizing the World: An Introduction to Visualization

7 Visualization

Video 1: The Power of Visualizations

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The slides from all videos in this lecture can be downloaded here: An Introduction to Visualization (PDF).

Quick Question

Normally, a scatterplot only allows us to visualize two dimensions - one on the x-axis, and one on the y-axis. In the previous video we were able to show a third dimension on the scatterplot using what attribute?

Color check

Shape close

Location close

Explanation On slide 3, we show the scatterplot from slide 2, but with the number of cylinders shown by the color of the points. This allows us to visualize a third dimension of our data.

Continue: Video 2: The World Health Organization (WHO)

Quick Question

Why is it particularly helpful for WHO to provide data visualizations? Select all that apply.

There is no other way to display information shown in visualizations like the Energy Consumption one. close

When communicating information to the general public, a visualization like the Energy Consumption one is much easier to absorb than a table of numbers would be. check

Visualizations can easily be used by policymakers and others who wish to present data from WHO. check

Explanation While there are other ways to display the data given in many visualizations (like tables), visualizations help to better communicate data to the public and can easily be used by others in presentations.

Quick Question

In this quick question, we’ll be asking you questions about the following three plots, that we saw in Video 1. We’ll refer to them as the “Scatterplot”, the “Histogram”, and the “US Map”.

The Scatterplot:

Scatterplot showing the miles per gallon of a car as a function of the car's weight.

The Histogram:

Histograms of different categories using Hubway data.

The US Map:

U.S. state map indicating unemployment by state by varying shades of red.

In the Scatterplot, what are the geometric objects?

Bars close

Points check

Lines close

Polygons close

Boxes close

Explanation The geometric objects for the Scatterplot are points, for the Histogram are bars, and for the US Map are polygons (the States). All three plots defined colors in the plot.

In the Histogram, what are the geometric objects?

Bars check

Points close

Lines close

Polygons close

Boxes close

Explanation The geometric objects for the Scatterplot are points, for the Histogram are bars, and for the US Map are polygons (the States). All three plots defined colors in the plot.

In the US Map, what are the geometric objects?

Bars close

Points close

Lines close

Polygons check

Boxes close

Explanation The geometric objects for the Scatterplot are points, for the Histogram are bars, and for the US Map are polygons (the States). All three plots defined colors in the plot.

All three of these plots defined a particular aesthetic property. What is it?

The x-axis label. close

The y-axis label. close

Different shapes for different types of observations. close

Colors. check

A legend. close

Explanation The geometric objects for the Scatterplot are points, for the Histogram are bars, and for the US Map are polygons (the States). All three plots defined colors in the plot.

Quick Question

In R, change the shape of your points to the number 15. What shape are the points now?

Circles close

Diamonds close

Crosses close

Squares check

Stars close

Explanation If you type: scatterplot + geom\_point(shape = 15) where scatterplot is the plot we created in the previous video, you can see that the points are squares.

Quick Question

Create the fertility rate versus population under 15 plot again:

ggplot(WHO, aes(x = FertilityRate, y = Under15)) + geom_point()

Now, color the points by the Region variable.

Note: You can add scale_color_brewer(palette=“Dark2”) to your plot if you are having a hard time distinguishing the colors (this color palette is often better if you are colorblind). To use this option, you should just add scale_color_brewer(palette=“Dark2”) to your plotting command right after geom_point().

One region in particular has a lot of countries with a very low fertility rate and a very low percentage of the population under 15. Which region is it?

Africa close

Americas close

Eastern Mediterranean close

Europe check

South-East Asia close

Western Pacific close

Explanation You can color the points by region if you adjust the command to the following: ggplot(WHO, aes(x = FertilityRate, y = Under15, color=Region)) + geom\_point() Most of the countries in Europe have a very low fertility rate and a very low percentage of the population under 15.

Back: Video 5: Advanced Scatterplots Using ggplot

Video 2: The World Health Organization (WHO)

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Video 3: What is Data Visualization?

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Video 4: Basic Scatterplots Using ggplot

In the rest of this lecture, we’ll be using the data file WHO (CSV). Please download this file to your computer, and save it to a location that you will remember. This data comes from the Global Health Observatory Data Repository.

An R script file with all of the commands used in this lecture can be downloaded here: Resource Unit7_WHO (R).

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Colors and shapes in R

If you want to see all of the available colors in R, type in your R console:

colors()

All of the available shapes are described in the following image:

This image comes from Cookbook for R. License: CC BY-SA. This content is excluded from our Creative Commons license. For more information, see https://ocw.mit.edu/help/faq-fair-use/.

The number 0 corresponds to an empty square, the number 6 corresponds to an upside down triangle, etc.

Video 5: Advanced Scatterplots Using ggplot

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