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2. All You Need to Know about Plots
Overview
This chapter will teach you the fundamentals of the various types of plots such as line charts, bar charts, bubble plots, radar charts, and so on. For each plot type that we discuss, we will also describe best practices and use cases. The activities presented in this chapter will enable you to apply the knowledge gained. By the end of this chapter, you will be equipped with the important skill of identifying the best plot type for a given dataset and scenario.
Introduction
In the previous chapter, we learned how to work with new datasets and get familiar with their data and structure. We also got hands-on experience of how to analyze and transform them using different data wrangling techniques such as filtering, sorting, and reshaping. All of these techniques will come in handy when working with further real-world datasets in the coming activities.
In this chapter, we will focus on various visualizations and identify which visualization is best for showing certain information for a given dataset. We will describe every visualization in detail and give practical examples, such as comparing different stocks over time or comparing the ratings for different movies. Starting with comparison plots, which are great for comparing multiple variables over time, we will look at their types (such as line charts, bar charts, and radar charts).
We will then move onto relation plots, which are handy for showing relationships among variables. We will...
Comparison Plots
Comparison plots include charts that are ideal for comparing multiple variables or variables over time. Line charts are great for visualizing variables over time. For comparison among items, bar charts (also called column charts) are the best way to go. For a certain time period (say, fewer than 10-time points), vertical bar charts can be used as well. Radar charts or spider plots are great for visualizing multiple variables for multiple groups.
Line Chart
Line charts are used to display quantitative values over a continuous time period and show information as a series. A line chart is ideal for a time series that is connected by straight-line segments.
The value being measured is placed on the y-axis, while the x-axis is the timescale.
Uses
- Line charts are great for comparing multiple variables and visualizing trends for both single as well as multiple variables, especially if your dataset has many time periods (more than 10).
- For smaller time...
Relation Plots
Relation plots are perfectly suited to showing relationships among variables. A scatter plot visualizes the correlation between two variables for one or multiple groups. Bubble plots can be used to show relationships between three variables. The additional third variable is represented by the dot size. Heatmaps are great for revealing patterns or correlations between two qualitative variables. A correlogram is a perfect visualization for showing the correlation among multiple variables.
Scatter Plot
Scatter plots show data points for two numerical variables, displaying a variable on both axes.
Uses
- You can detect whether a correlation (relationship) exists between two variables.
- They allow you to plot the relationship between multiple groups or categories using different colors.
- A bubble plot, which is a variation of the scatter plot, is an excellent tool for visualizing the correlation of a third variable.
Examples
The following diagram...
Composition Plots
Composition plots are ideal if you think about something as a part of a whole. For static data, you can use pie charts, stacked bar charts, or Venn diagrams. Pie charts or donut charts help show proportions and percentages for groups. If you need an additional dimension, stacked bar charts are great. Venn diagrams are the best way to visualize overlapping groups, where each group is represented by a circle. For data that changes over time, you can use either stacked bar charts or stacked area charts.
Pie Chart
Pie charts illustrate numerical proportions by dividing a circle into slices. Each arc length represents a proportion of a category. The full circle equates to 100%. For humans, it is easier to compare bars than arc lengths; therefore, it is recommended to use bar charts or stacked bar charts the majority of the time.
Use
To compare items that are part of a whole.
Examples
The following diagram shows household water usage around the world:
...Distribution Plots
Distribution plots give a deep insight into how your data is distributed. For a single variable, a histogram is effective. For multiple variables, you can either use a box plot or a violin plot. The violin plot visualizes the densities of your variables, whereas the box plot just visualizes the median, the interquartile range, and the range for each variable.
Histogram
A histogram visualizes the distribution of a single numerical variable. Each bar represents the frequency for a certain interval. Histograms help get an estimate of statistical measures. You see where values are concentrated, and you can easily detect outliers. You can either plot a histogram with absolute frequency values or, alternatively, normalize your histogram. If you want to compare distributions of multiple variables, you can use different colors for the bars.
Use
Get insights into the underlying distribution for a dataset.
Example
The following diagram shows the distribution...
Geoplots
Geological plots are a great way to visualize geospatial data. Choropleth maps can be used to compare quantitative values for different countries, states, and so on. If you want to show connections between different locations, connection maps are the way to go.
Dot Map
In a dot map, each dot represents a certain number of observations. Each dot has the same size and value (the number of observations each dot represents). The dots are not meant to be counted; they are only intended to give an impression of magnitude. The size and value are important factors for the effectiveness and impression of the visualization. You can use different colors or symbols for the dots to show multiple categories or groups.
Use
To visualize geospatial data.
Example
The following diagram shows a dot map where each dot represents a certain amount of bus stops throughout the world:
Figure 2.39: Dot map showing bus stops worldwide
Design Practices
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What Makes a Good Visualization?
There are multiple aspects to what makes a good visualization:
- Most importantly, the visualization should be self-explanatory and visually appealing. To make it self-explanatory, use a legend, descriptive labels for your x-axis and y-axis, and titles.
- A visualization should tell a story and be designed for your audience. Before creating your visualization, think about your target audience; create simple visualizations for a non-specialist audience and more technical detailed visualizations for a specialist audience. Think about a story to tell with your visualization so that your visualization leaves an impression on the audience.
Common Design Practices
- Use colors to differentiate variables/subjects rather than symbols, as colors are more perceptible.
- To show additional variables on a 2D plot, use color, shape, and size.
- Keep it simple and don’t overload the visualization with too much information.
Activity...
Summary
This chapter covered the most important visualizations, categorized into comparison, relation, composition, distribution, and geological plots. For each plot, a description, practical examples, and design practices were given. Comparison plots, such as line charts, bar charts, and radar charts, are well suited to comparing multiple variables or variables over time. Relation plots are perfectly suited to show relationships between variables. Scatter plots, bubble plots, which are an extension of scatter plots, correlograms, and heatmaps were considered.
Composition plots are ideal if you need to think about something as part of a whole. We first covered pie charts and continued with stacked bar charts, stacked area charts, and Venn diagrams. For distribution plots that give a deep insight into how your data is distributed, histograms, density plots, box plots, and violin plots were considered. Regarding geospatial data, we discussed dot maps, connection maps, and choropleth...
