Probably a reference to Yering Station, leased by Paul de Castella. de Castella and his family were friendly with Barak.
The graph displays the other subjects mentioned on the same pages as the subject “Castellas”. If the same subject occurs on a page with “Castellas” more than once, it appears closer to “Castellas” on the graph, and is colored in a darker shade. The closer a subject is to the center, the more "related" the subjects are.