The bar chart shows what percentage of the site each section represents.  This is based on the number of entries in each section and is shown by the lighter grey bars.

Then compared to these are the number of visits to each section, which are shown by the darker grey bars.  The number of visits to each section are shown as percentages of the number of visits to the site as a whole.

What this does seem to show is that the individual group listings are still the main use of the site. This is re-assuring as directory entries were the original reason for setting up the site.