Earlier, I said I’d discuss how to choose between bar charts and column charts. I make my choice based on three main considerations – subject, shape, and space.
Some things are more intuitively horizontal, and some are more intuitively vertical. If you were to make a chart that showed the heights of various children, then intuitively that should be a (vertical) column chart because a taller child would be represented by a taller bar. Alternatively, if you were to make a chart that showed how far various children ran in a timed dash, then intuitively a (horizontal) bar chart would be the way to go, because you want people to be thinking in terms of horizontal distance.
When dealing with a subject that has an intuitive direction, then it’s better to go with that direction or people will have trouble instantly grasping the meaning of it. However, not all subjects have an intuitive direction. If you were to make a chart that showed how many books children read during a summer reading program, it wouldn’t intuitively matter whether it was horizontal or vertical. In this case it’s better to look at the other two considerations.
A chart of this type has two axes: items and values. Each item has a value. In the charts described above each child would be an “item”, and their heights, running distances, or books read would be the “value”.
These axes can be thought of as sides in a rectangle. Like rectangles, most have a long side and a short side. If there are many items and only a small variance in values, then the items axis is the long one, and the values axis is the short one. For example, if a chart depicted the GPA for each student in a class of 30, the list of students (Student 1 through Student30) would logically take up more room than their values (0 through 4.0).
However, if you had a group of six people trying to lose 150 pounds each, then a chart showing their progress would need more room for the value of pounds lost so far.
Once you know which axis is long and which is short, it’s time to look at the space available. Is it a sheet of paper that will be viewed portrait-style, with the long edges on the sides and the short edges at the top and bottom? Then you want to put your long axis along the side, and your short axis along the bottom. This would make the GPA chart a (horizontal) bar chart, and the weight-loss chart a (vertical) column chart.
Is it a website that is likely to be viewed on a monitor, or is it going to be projected onto a screen for an audience? Both of these situations result in a space that is wider than it is tall. Therefore the long axis goes along the bottom, and the short axis goes along the top. This would make the GPA chart a (vertical) column chart, and the weight-loss chart a (horizontal) bar chart.