The cumulative view tends to be more useful than the instantaneous view.
From my look at your cumulative view, it looks like you've got a lot of nearby 2.4GHz activity in the channel 1 and channel 8 ish region, while the area right below channel 6 tends to be least used.
The graph shows a heat map of what receive strengths are most often perceived at each frequency. A Ruckus AP generally has a noise floor on the order of -95 dbm or lower (e.g. more negative), so if you powered up your Ruckus in a completely clean environment you'd expect to see one big red line at -100 or so.
