1. A method comprising: providing a candidate category hierarchy, including candidate categories, and a mapping between reference pages and the candidate categories, including mapped reference pages; obtaining population usage data of each of the mapped reference pages; using the population usage data to determine a population traffic metric for each of the candidate categories; generating population categories from the candidate categories by using the population traffic metric of each of the candidate categories; and producing a population category hierarchy including the population categories.
1. A method comprising: providing a candidate category hierarchy, including candidate categories, and a mapping between reference pages and the candidate categories, including mapped reference pages; obtaining population usage data of each of the mapped reference pages; using the population usage data to determine a population traffic metric for each of the candidate categories; generating population categories from the candidate categories by using the population traffic metric of each of the candidate categories; and producing a population category hierarchy including the population categories. 13. The method of claim 1 , wherein generating the population categories from the candidate categories by using the population traffic metric comprises: identifying a first candidate category with a population traffic metric that is lower than inclusion threshold but higher than a deletion threshold; identifying a second candidate category also with a population traffic metric that is lower than the inclusion threshold but higher than the deletion threshold; and merging the first and second candidate categories into a population category.