At a Glance Section on the Site

G'day, I have been using the site for a while now but I still can't figure out how to use the line graph in the "At a glance" section that appears on every page of the tracks you search. For example, on The Brisbane Water National Park page of the Site, with reference to tracks, it states "Fire trail 15 for 30kms 89% Single track Enclosed 1 for 0.4kms 1% Exposed 2 for 3.1Kms 9%. I've been trying to work it out on my own for a few years and I am baffled. Does it have something to do with how much of that 30kms is ride able because of current conditions, or obstacles like steps etc? Thanks in advance