When describing tobacco barns, a "room" is the space between two sets of tier poles, running from top to bottom. Barns are measured in rooms, as in "3-roomer" (a barn with two columns of tier poles running though the middle of it. The barns standing at Julia's farm in 2008 are "5-roomers", which are considered unusually large.
The graph displays the other subjects mentioned on the same pages as the subject “room (barns)”. If the same subject occurs on a page with “room (barns)” more than once, it appears closer to “room (barns)” on the graph, and is colored in a darker shade. The closer a subject is to the center, the more "related" the subjects are.