1. A method of training an automated classifier to identify topical categories of content items of a content set using a device comprising a processor and having access to at least one human classifier, the method comprising: executing on the processor instructions configured to: for respective content items of the content set: using the automated classifier, identify at least one topical category for the content item with a classification confidence; for respective content items having a classification confidence for a selected topical category that is below a classification confidence threshold: send the content item to a human classifier including the selected topical category into which the content item has been classified, and upon receiving from the human classifier at least one user-selected topical category associated with the content item, store the content item in a training set associated with the at least one user-selected topical category; and train the automated classifier using the training set.