1. A computer-implemented method, comprising: receiving, by a data processing device, data specifying a search query that was submitted by a user; determining, by a data processing device, a particular search topic with which the search query is associated; determining, by a data processing device, that the particular search topic with which the search query is associated has been classified as an underserved topic, the underserved topic being a search topic for which a relative topic corpus quality measure is less than a threshold value, the relative topic corpus quality measure being a relevance measure for documents that are included in a topic corpus for the search topic relative to a query search volume value for queries that have been identified as being associated with the search topic, the query search volume being a value that is derived from a number of times that the search query has been received; and providing, by a data processing device and in response to receiving the search query, data that cause presentation of a notification that the search query is associated with an underserved topic.