Why is the subject area filter not available for Research Areas and Topics / Topic Cluster entities in Overview?

Most Topics, Topics Clusters and Research Areas are by design about a specific subject area, built from the properties of individual articles. The subject area filter uses journal classifications as a grouping mechanism and would therefore offer little insights into these entities. The inclusion of the subject area filter would also increase our weekly processing timesopens in new tab/window, which is why we chose not to include it.