In your library this might be an atlas, an encyclopedia, or even an almanac. When answering a question over the phone it is always a good idea to tell the caller the name and date of the book you are reading from. Even if world atlases have information that can be found elsewhere, they are useful to have. They gather a lot of geographical information in one place, and the maps are often larger and more detailed than those found in encyclopedias. In addition, atlases often contain thematic maps and graphs that give more information than just geographical locations.
Most world atlases have both political maps and relief maps.
The former show national and other political boundaries, and cities, while the latter show the details of the landscape. Coverage of the United States differs from atlas to atlas. In some, each state has a page to itself, while in others each map shows a region containing several states. Map coverage of the larger metropolitan areas of the world also differs. Some atlases have many maps of this sort for both American and foreign metropolitan areas.