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.