I have an interface that allows you to pull data related to a number of topics, but then also allows you to be more specific about what aspects of those topics you want information on.
For example, say a general category is "weather" and you can pull information on weather generally. One of the more specific aspects might be "Southern hemisphere weather." Additionally, there might be entries such as "weather monitoring agencies;" that is, entries that are related but not direct subcategories.
I'm looking for a verb that means "to be more specific," by selecting one of these sub- or related categories. I considered refine but that to me implies sifting or filtering, as opposed to delving deeper. Drill down is a more idiomatic approach, but sounds far too informal.