Charts and Graphs

How to pick a chart type – Charting 101

Last updated on June 5, 2019

Chandoo

Bar chart or Line? Scatter plot or box plot? These are the questions we ask ourselves when we set out to make a chart. In this article let me tell you how to pick a chart type so you can make best charts for every situation.

Why is it important to pick right chart?

Because right charts lead to right decisions. We use charts to tell stories, evaluate alternatives, understand trends or find-out if everything is normal. So, an incorrect charting choice can lead to poor judgment of the messages where as a correct chart can lead to right and faster decisions.

How to pick a chart type:

Chart making process can be divided in to 4 steps

Find-out what you want to say?
(Re)arrange the data
Prepare the chart
Format the chart

1. What is the purpose of this chart?

This is the first and most important step in chart preparation. You must ask yourself, “what is the purpose of this chart?”. Once we know the clear reason why the chart should exist, we will naturally be able to select the correct chart type for that reason.

But I realize that finding the reason itself can be a bit tedious. So I have listed down 6 common reasons that we often have to make a chart:

to Compare
to show the Distribution
to explain Parts of the Whole
to tell the Trend over time
to findout the Deviations
to understand the Relationship

Let us understand these reasons along with the type of charts that go well with these.

1. To Compare:

What it means? You want to compare one set of value(s) with another.
Examples:

Performance of Product A vs. Product B in 5 regions
Interview performance of various candidates

Charts that can be used for this reason:

Bar Charts,
Column Charts
Scatter Plots
Pie Charts
Line Charts
Data Tables

2. To Show the Distribution

What it means? You want to show the distribution of a set of values (to understand the outliers, normal ranges etc.)
Examples:

Distribution of Call waiting times in a call center
Distribution of bugs found in 10 week software testing phase

Charts that can be used to show distribution:

Column Charts
Scatter Plots
Line charts
Box Plots

3. Parts of Whole

What it means? You want to show how various parts comprise the whole
Examples:

Individual product sales as a percentage of whole revenue
Browser types of customers visiting our website

Charts that can be used to show Parts of Whole:

Column Charts
Bar Charts
Pie Charts
Data Table

4. Trend over time

What it means? You want to understand the trend over time of some variable(s).
Examples:

Customer footfalls on the last 365 days
Share price of MSFT in the last 100 trading sessions

Charts that can be used to show Trend Over Time:

Column Charts
Line Charts
Data Table

5. Deviations

What it means? You want to see which values deviate from the norm.
Examples:

Failures (or bugs) in the context of Quality Control
Sales in Various Stores

Charts that can be used to show Deviations:

Column Charts
Bar Charts
Line Charts
Data Table

6. Relationship

What it means? You want to establish (or show) relationship between 2 (or more) variables
Examples:

Relationship between Search Phrases and Product Purchases in your website
Relationship between in-store sales and holidays

Charts that can be used to show Relationship:

Scatter Plot
Line Chart
Data Table

How to pick a chart type when you have more than one reason for the chart?

Simple, use common sense. If I were you, I would either cut down the messages to one or make 2 charts (each conveying one message). If that is not possible, I would consider using dynamic charts or combination charts.

2. (Re)arranging the Data

Even when we know the message and corresponding chart, sometimes, our data may not support us. We then have to rearrange the data. Using excel formulas, pivot tables, tables and data cleaning tools we can easily massage the data.

Once we have the data in required format, we proceed to step 3.

3. Prepare the chart

Since you have already picked the chart type in Step 1, this is very straight forward. Most of the regular charts are available in MS Excel as default charts. You can insert them with few clicks.

But for some special chart types, you may have to prepare the chart by helper series, formatting etc.

4. Format the chart

While most formatting is done as per individual taste, there are some ground rules that apply on almost all charts. Here they are,

No non-zero axis scale on bar charts [reasons and discussions]
Make subtle grid-lines (or remove them) [how to remove grid lines]
Add labels to important points [labeling techniques]
Add descriptive, bold titles
Position axis, scales at the right places (for eg. y-axis to the right on a large time series chart)
Use simple, easy colors

A final word:

The ideas in this post are meant to be guide lines, not final words in the world of visualization. While these rules can help you make a good chart, a great chart take so much more. Knowledge of your data, Passion for what you do and Genuine focus on your audience’ needs can make your chart truly outstanding. All the best.