10 x 10 tips to improve your (Excel or not) charts: Line charts

Following the 10 x 10 post series on tips for better charts, these are the 10 tips for line charts:

  1. Don’t use line markers unless you really need them to identify b&w printed charts;
  2. Don’t use a legend; directly label the series, instead;
  3. If you can’t easily see the pattern of each series you may have too many;
  4. In a time series, the spacing between markers in the x-axis should be proportional. For example, if you have data for years 1980, 1990, 2000 and 2008, the spacing between 2000 and 2008 should be smaller than between other dates; if you can’t do it with line charts use a scatter plot;
  5. If you are comparing two series like imports/exports or profit/expenses, chart the differences, not the actual series (or at least add a small chart with the differences, below the main chart;
  6. If you are comparing two time series with very different units of measurement, consider using a logarithmic scale;
  7. You don’t have to start the Y-axis scale at zero; break the scale if you need;
  8. If you are using different line styles you may be emphasizing some series more than the others; make sure that’s consistent with your users needs (emphasize what is important);
  9. Add a trend line (make sure the trend is plausible…);
  10. Don’t use line charts for categorical data; if you need a profile chart use a scatter plot and switch axis.

Feel free (and I would appreciate) to comment or add your own tips…

6 thoughts on “10 x 10 tips to improve your (Excel or not) charts: Line charts”

  1. I think it goes without saying that you should keep the chartjunk to a minimum. e.g. tick marks, gridlines, background fill, text formatting, heaven forbid – background image, etc.

    The more lines you have the smaller the weight of the line should be. If you only have two series, use a higher weight (just don’t overdo it).

    Add some valuable insight below the chart regarding outliers or significant changes in the trend.

  2. Thanks Tony. From the communication point of view the idea of changing the weight of the line is very interesting. The other tips should be followed regardless of the type of chart.

  3. I don’t like the labels on the charts because I think it makes it look to busy. I think a legend is okay.

    One tip I have is when you have a group of charts – use the colors consistenly. For instance, if Blue means “Russia” on one chart then it should mean “Russia” on all charts in that package. I’ve seen people vary the colors – sometimes just not realizing they had done it. It causes confusion for the end user.

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