The cartographer is the 'author' of the map. In the printed index, this is a two-tiered system. In the electronic indexes, the primary term and secondary term can be searched together or separately. The primary or main term is a geographic locator, the secondary is a subject descriptor. The geographic locators selected to index a map vary with the focus and scale of the item.
Primary terms are generally geographical.
However, proper names may also be primary terms. Proper names of individuals should be searched last name, first name. Proper names may also be used when the subject is difficult to express or locate under a single geographic entry, as with the Gulf Intracoastal Waterway. In the latter case, the subject entry will also appear under a geographic heading. The secondary terms refer to major subjects found on maps, such as, routes and trails, oil wells, railroads, or to a type of map, for example, survey map, highway map, nautical chart, general map.