Are there situations where a vertical bar chart is preferable to a horizontal one?

Question

I hardly see what kind of advantage a vertical bar chart could have over a horizontal one (edit: by "horizontal bar chart", I mean a chart with bars oriented horizontally). On the other hand, vertical bar charts are so prevailing that it makes me wonder if I'm just lacking imagination or experience.

In particular, I'm wondering:

• If you have many categories to plot, the labels for each category on a horizontal bar chart are easier to read (e.g. you don't have to move your head to read a vertical or rotated label). Are there situations where this isn't true?

• If you have long labels for the categories, an horizontal bar chart requires less line breaks than a vertical bar chart. Thus, a horizontal bar plot is probably easier to read. Again, are there situations where this isn't true?

These are two examples where horizontal bar charts are likely superior, but maybe there are other situations I'm not thinking of, and where vertical bar plots have an advantage. I'd be interested to learn about that. (This blog post talks about the issue, if you're interested in some visual examples and my previous examples are not clear - note that I'm not a SAS user, by the way).

A practical stake for me is work-related, i.e. automation of graph generation. Recently I've been wondering if I should make horizontal bar charts the default (as it's easier to deal with labels overlap and so on, it would save me some programming time). On the other hand, I don't want to generate incorrect or misleading data visualizations, or run into other problems I did not anticipate. Hence my question.

I'm definitely not looking for answers similar to "I find vertical bars ugly" or other opinion-based answers. I'm looking for practical, objective issues that members of an audience may encounter with horizontal bar charts, but not with vertical bars. Which makes me think that I'd also be interested in references on the subject - peer-reviewed publications based on experiments would be perfect.

Edit:

I realize that my question assumes we're dealing with graphs in English or other languages where vertical writing is not an option. It is because the practical issue that caused my question does not involve languages like Japanese or other East Asian languages where vertical writing is possible. However if someone has information about graphs in those languages, and how the problem possibly differ compared to other languages, I'd be curious to hear about it (I guess that the option to write vertically simply gives more flexibility and makes things easier relative to vertical bar plots, but as I'm not familiar at all with those languages I may be wrong). A word or two about those languages might be also directly helpful to other people than me.

By the way, thanks to all the people who answered so far, it has been interesting and helpful.

Answer 1

If you have "many" categories, then a vertical chart will be wider than it is tall. A horizontal chart will be taller than it is wide. (Note the potential for confusion what "vertical" and "horizontal" mean, per my comment.)

Which one makes more sense depends on your situation. Mobile phone screens are usually in portrait mode and would work better with horizontal charts. Laptops or desktop computer screens are usually in landscape orientation and may work better with vertical charts. If you are writing a paper, which one makes best use of your page real estate depends very much on the number of categories.

I would assume that humans are better at comparing the length of horizontal bars than the height of vertical ones, but do not know of any research on this. I am sure someone has already looked at this.

Answer 2

The accepted answer from @Stephan Kolassa is fine by me, but unsurprisingly more can be said.

First, let us clear out of the way a small question of definition. To some authors, bar charts are those with horizontal bars, while vertical bars define a column chart. If you think this distinction is somewhere between unnecessary and absurd, I agree with you. But it's far from dead, although I sense its use is declining. In what I see, the more common distinction is -- as in the question title -- between horizontal bar charts (bars go from left to right by default) and vertical bar charts (bars go from bottom to top by default). Neither term rules out (e.g.) pairing of bars, as in so-called population pyramids showing age distribution of population with bars for numbers of males and females laid back to back.

The leading point in my experience over whether to use horizontal or vertical bars is that designers should show text labels legibly, as mentioned in the question. All bar charts need clear explanations of the categories shown. This is usually easier with horizontal layout. With a vertical layout, some people use a legend instead of text by each bar. At best that is an awkward solution, as are some other work-arounds in common use, such as very small font sizes, text running at an angle (even vertically), or abbreviations verging on the cryptic. This comment, however, bites most, or even only, if text in the language used is customarily shown horizontally.

Conversely, some very concise abbreviations have become so widely accepted that they suit vertical bars, including chemical element symbols such as Cu and Zn and two-letter codes such as AL and AK for states of the United States.

Yet again, as @matt_black flags in his answer, some bar charts don't need labels for every bar, as is often true if bars are for a series of dates and mental interpolation is easy enough.

In addition, two points arise quite commonly.

In statistical graphics, vertical bars match a common convention that whatever is the outcome or response of interest is usually plotted vertically unless there is good reason to do otherwise.

Occasionally, plotting vertically or horizontally may seem natural for other reasons, even if pure convention or just a matter of psychology. Thus a bar chart for heights of buildings would seem very odd if presented horizontally, while durations (lengths of time) might seem better suited to horizontal layout.

Answer 3

One issue is to synchronize intuition with the convention of graphing mathematical functions with the dependent variable on the y-axis, and the independent variable on the x-axis (i.e., matching a vertical bar chart). For instance, if the data is quantitative, it's easier to eyeball whether it matches some known probability distribution previously studied. Here's an example from the Weiss Introductory Statistics textbook:

Answer 4

The conventional wisdom here is based on the readability of categorical labels which are often hard to read if the text is not horizontal.

But this can sometimes be unhelpful in context where the categories from part of a regular series. For example, if the plot is of monthly performance over several years. Here, not every bar needs to be labelled with the full name of the month as the reader of the chart knows the sequence of months and the reader can interpolate the specific months easily without the labels (eg when year boundaries are labelled). Plus, for data like time series, the common charts show them from left to right so the bars may be interpreted more naturally in that orientation.

So the penalty of readability for a chart oriented this way is not a notable issue.