2. The method of claim 1 , wherein the population usage data includes timestamps and a total number of visits to each of the mapped reference pages wherein the timestamps are used to estimate a time that visitors spent on each mapped reference page.
2. The method of claim 1 , wherein the population usage data includes timestamps and a total number of visits to each of the mapped reference pages wherein the timestamps are used to estimate a time that visitors spent on each mapped reference page. 4. The method of claim 2 , wherein determining the population traffic metric includes summing the total number of visits to each of the mapped reference pages to a particular one of the candidate categories.