These are 10 basic tips for column and bar chart design:
- A column chart is not a skyline: if you can’t see the individual patterns, consider removing some series or create several smaller charts;
- If you are charting categorical data sort the columns; if there is more than one series, allow the user to sort the data herself;
- If you are displaying time series, column charts are not interchangeable with line charts: column charts allow you to compare individual data points, while a line chart shows the trend; be sure to select what your audience wants to see;
- For target/actual series (like budget/actual) overlap them but make sure they can’t be taken for stacked bars; you can do it by using a different column width for each series or by setting filling to none (usually the target series);
- Use horizontal bar charts when x labels are too large to be correctly displayed;
- The y axis scale should start at zero; this is particularly important if you are using bar charts; make sure you have a (very) good reason to break this rule;
- If you really need to label each column try to minimize its impact; in Excel 2003, select Format Data Labels / Alignment / Label Position: Inside Base;
- Don’t use multiple colors for a single data series;
- Avoid stacked bar charts;
- Use category/subcategory to label the x axis. For example, instead of having Mar-2008, Apr-2008… use Mar, Apr and place 2008 in the second line.
As usual, feel free to add your own tips in the comments.
It would be useful to see examples to accompany the text.
Stanley: in this specific series I am not planning to add example charts because each tip should be linked to a more detailed post. But yes, there should be more charts in the blog. I’m working on it.