The average values (as opposed to the most frequent value, as done in [6]) were chosen as the reference (``anchor'') point because of their stability.
Tests performed using the most frequent value would fail in the presence of a page with many small or large connected components (as in an index page for example, where many dots can be present in relation to the number of letters). Since a stable reference to some point in the WH-Map is needed, the average values should be.
Therefore, the reference point is calculated: