10 x 10 Tips to improve your (Excel) charts: formatting

This is the second of 10 posts where I’m listing tips for better charts. Please take a look at the first post where the project is discussed. These are my chart formatting tips:

  1. Use the right chart type for the data and the problem;
  2. Apply sound design principles;
  3. Use color strategically: mute axis and grid lines by graying them out; gray out some contextual data also; use soft colors; use saturated colors sparingly and with a clear purpose of emphasis;
  4. What the users see is not what you see in your monitor: if needed, test for other monitors and output formats (b&w print, color print, PDF, overhead projector);
  5. There is no rational justification to use pseudo-3D charts and other dubious effects (gradients, glow…), so never use them if you what to be rational;
  6. Use a clear font;
  7. Don’t emphasize everything (for obvious reasons);
  8. The y axis scale should start at zero; this is particularly important if you are using bar charts; make sure you have a good reason to break this rule;
  9. A chart is not a table: by labeling every single data point you make it harder for the user to search for trends or patterns; if you have to, place the labels where they can do no harm;
  10. Annotate: Add labels for the last, the lowest, the highest or any other relevant data point; add data or comments where appropriate;
  11. Bonus tips: Use smaller charts and never accept the Excel defaults;

What are your best chart formatting tips? Please share them in the comments!

5 thoughts on “10 x 10 Tips to improve your (Excel) charts: formatting

  1. I don’t agree with 8, and I think obsession with this rule (which you obviously aren’t as you say it can be broken) leads to some idiotic charts.

    The reason it can be broken is because sometimes in the two series you are comparing there is a constant base level, and it is the change from that level which is interesting. Thus you can quite legitimately (in my view) start the chart around the peak of that base level.

  2. Matthew: by default the origin should be zero. I agree with you: there are charts where it doesn’t make sense or is plain stupid. But too often we see misleading column charts because the scale is not shown and the reader can’t verify where it starts.

    So, break the rule when you have to, but make sure that improves the chart.

  3. Jon: it is very specific to column charts, isn’t it? Probably I’ll replace it and move it to the tips on column/bar charts.

  4. Excel has a nasty habit of autoscaling the Y axis to give nice amounts of white space. I think a good corollary to 8 is that the Y axis should end at the maximum possible value, if there is one. I do a lot of work displaying student assessment data, and if the test is out of 100 points, there’s no reason for the chart to go to 120. Yet so many student data charts do, because (rule 11) that’s the Excel default.

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