a book which alphabetically names and describes the places in a specific area.
An example would be a gazetteer of a county would name and describe all of the towns, lakes, rivers, and mountains in the county.
So how would this be a good genealogical tool?
It can help you located towns within a state and a county.
It can tell you about what life was life during a particular time frame. Maybe you have heard that a family member did a lot of hunting or fishing a particular lake or mountain. Is that lake in the town in which you believe your family is from? Remember there are lots of towns and counties in different states with the same names. Some states have multiple towns with the same name. This would be a great tool to narrow it down.