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.
8. The method of claim 1 , wherein generating the population categories from the candidate categories includes adding or splitting candidate categories.