In Tufte’s The Visual Display of Quantitative Information, and recently on his blog, he discusses the use of slopegraphs to show change over time. They are highly effective because you have both the text (the reader would likely want to know the individual values), the sorting, and the slope which allows you to understand the magnitude of change and those countries that bucked the trend of increasing over the time period.
Creating them however is more of a challenge. While it would seem that with some creative label calculations combined with a line chart would suffice, in this data set (and many I would suspect) the line ends are too close together (see first tab below). In fact Tufte has manipulated the positioning of the line ends and labels manually to provide some spread on the axis. This, of course, provides a challenge if you want to automate the process in any way. I approached this by calculating the start and end positioning of each country using a table calculation (see tab 2), and using this to position the countries (tab 3). Of course, this loses the slope information and only shows the position change. To add the slope back in I use a calculation that combines both the index and original value to ensure that the lines cannot end too close to each other (tab 4). I then manually moved the labels to a better position to create the final slopegraph (tab 5).
Comments on the workbook: 1. Note that the label calculation is has the left() statements because of issues when you use extracts – 46.8 turns into 46.8000000001 or similar. 2. I spent ages trying to get this to work, but as soon as I put the label (country plus value) on the label shelf, it would alter the table calculation (I don’t know why as it’s a string). Making the label an attribute stopped that. 3. This method affects the slope of the lines to some degree. Another option would be shift the correct slopes up and down, thus making the vertical positioning slightly wrong (EDIT: This method now appears on sheet 5a. It turns out that this is really hard to get right – the order messes up, and you end up moving everything around – try changing the parameters yourself and getting the spacing and order correct. Looking back at the original, Tufte changes the slope as per my first method).