AER Style Guide > AER Style > Formatting > Figures and Tables > Figures > Charts

Charts

The AER has professional graphic designers on staff. You can reach them by emailing Design.Services@aer.ca.

Some general principles for chart design can be had in a number of places:

Wong, Donna M. The Wall Street Journal Guide to Information Graphics: The Dos & Don’ts of Presenting Data, Facts, and Figures. New York: W. W. Norton and Company, 2010.
Google’s guide to data visualization

General Guidelines

Avoid running type vertically or on an angle. If necessary, run vertical type up the chart from bottom to top.

Left: Horizontal axis label (preferred); Right: Vertical axis label

Avoid all caps and ending a line with a hyphen.
In most cases the x-axis should start at zero.
Where possible label directly on or beside chart elements with black text. When there are many items, place the legend at the bottom of the figure left aligned to the y-axis.
Ensure high contrast in values to distinguish chart elements. Do not use crosshatching or other stylistic elements to distinguish categories.
Y-axis scale should be chosen so that the graph occupies roughly two-thirds of the chart area. Use increments people naturally use when counting such as 0, 5, 10, 15, 20, etc.
Use comparable scales when contrasting two or more sets of data in different ranges. The ranges of y-axis on both charts should represent the same percentage change.

The range of both charts is a 25% increase (20 to 25 and 100 to 125)

Do not use three-dimensional charts, they easily misrepresent data and are hard to read accurately.
When colouring charts generally colour as gradients from light to dark or dark to light. Do not alternate.

Gradients should go in one direction and not alternate

Label items directly only when there are two or fewer categories. Otherwise, use a legend.

Only label items directly when there are one or two categories. With more, use a legend.

Use line charts for continuous data.
Keep line charts to four or fewer lines. With more, use an array of charts so that each line is clear.
In colour charts the most important line should be one colour and the rest of the lines should be shades/tints of a second colour.
In black and white charts, the darkest plotted line should represent the most important data series.
A grey background can be used to identify the estimated values or negative zone.

Use bar charts for discrete quantities.
Bar charts always start at 0 baseline.
Always label the value of a bar if it is close to zero.
Width of the bars should be about twice the width of the space between the bars.
Bars in a single chart should be the same colour and shade since they measure the same variable.
Don’t use multiple colours to represent the same kind of data.
Don’t use red for positive numbers in a bar chart.
Don’t use different colours or colours on the opposite side of the colour wheel in a multiple-bar chart. The colour contrast distracts the reader from the data.
Colour lightest to darkest for bar charts with multiple categories and order legend items in the same sequence they appear in.

Colour order in bar charts

If the data points are close in value and hard to tell apart, try plotting in percentage change.

Use when ranking items by the same characteristic.
Avoid grid lines and scale, instead label at the end of each bar.
For a long list of bars, label the data points flush right and use thin rules every 3 to 5 items to help read across.
Order largest to smallest or vice versa.
A specific bar can be highlighted with a different shade to draw attention to important data.

In general pie charts should be avoided. Only use pie charts if the total adds up to something of significance such as a target value.
Order the segments by placing the largest segment at 12 o’clock on the right. Order the rest of the segments by placing the second biggest slice at 12 o’clock on the left; the rest would follow counterclockwise the smallest slice falling near the bottom of the chart.
A donut pie chart can be used to display the total value inside the pie.

Don’t use a pie chart with more than five segments. If there are more than five, combine the smaller and less significant segments to create the fifth slice and label it “other”. Alternatively use a stacked bar chart instead.
Label percentage values. If a segment is too small, use a line attached to the slice and label the line.
Never pullout a segment of pie to highlight, use a colour or high contrast value instead.
Keep the shading simple but use different shading or colour to highlight one or two important segments.
Never breakdown one segment of a pie by showing another pie. Always use a bar chart instead of another pie.