Users don’t know or cannot recall the name or location of a geographic boundary and need help to discover or find places based on a hierarchical structure.
Browsing is a common human behavior to orient oneself, e.g. people typically scan the table of contents of a new book or magazine and similarly browse the aisles of a book store for genres. Browse Geographies is an alternative means of navigation to using the map or a search. The latter ones are powerful in their own respect but have drawbacks if users aren’t geography savvy or don’t know exactly what they are looking for or the correct spelling.
Browsing is an exploratory, information seeking strategy that is especially appropriate for new or unknown domains. Providing a hierarchical representation of the content structure will help users understand and navigate unknown or forgotten geographical relationships. This is especially important with uncommon geographies or unfamiliar spaces, e.g. postal codes within a county, state parks within an administrative unit, Indian reservation in a state, school districts within a county, etc.
Display a list of geographies that represent the top level of the hierarchy. Allow users to select a geography to reveal its child geographies. Further nesting is acceptable if a clear back (up) navigation is available.
Consider removing geographies if they are not relevant to the user’s task or to show that only a few out of the whole have information within, e.g. if only 7 out of 50 states have store locations then it’s a good practice to remove the remaining 43.
Vice versa, if most geographies have content but some don’t, leave all geographies in place but indicate which ones are empty, e.g. gray out or not clickable
Consider adding counts to the geographies to indicate the volume a user can expected in each bucket. This is more useful for uncommon structures (school districts in counties) than political hierarchies (counties in states)
Different map interactions can occur at each step of the navigation through the hierarchy, e.g. the map could zoom to that geography or the selected geography could serve as the input for a spatial inquiry.
 Tognazzini, Bruce “Tog”: Browse vs. Search: Which Deserves to Go? – http://www.asktog.com/columns/085BrowseVsSearch.html