If you've every been involved in advertising you'll know that to create an effective print advert you need to use your space wisely. You don't use every inch of white space just because you can. You leave some “breathing room” so people can digest your message.
Early on mapmakers quickly realised that once the issue of scale had been addressed this was obviously going to result in some empty space appearing on the intended map in production. So like any good marketing push they set about filling such space with a variety of devices including cartouches, vignettes or insets. Collectively grouped we can refer to these as map ornamentation. This was presented in a way that wisely used the space available to capture attention and convey the message - There's nothing new under the sun!
One such device is the cartouche. To quote Wikipedia "A cartouche in cartography is a decorative emblem on a globe or map. Map cartouches may contain the title, the printer's address, date of publication, the scale of the map and legends, and sometimes a dedication. The design of cartouches varies according to cartographer and period style." That just about covers it.
Above: c1758 Jacques Nicolas Bellin "Suite du Brasil pour servir a l'Histoire generale des voyages : villages d'Indiens et missions ruinees, tire de la carte d'Amerique de M. Danville" (Continuation of Brasil to be used in the general history of travels: Indian villages and ruined missions, drawn from Mr. Danville's America map).
HOW TO IDENTIFY: It's good to examine the cartouche carefully, especially on early maps where they are more elaborate. what does it tell you? Is the design style in keeping with the period the map is from? But its not just about design style, often the official title of the map is found within the cartouche. Other useful information sometimes recorded within the cartouche will include the mapmaker, publisher, date and place of publication, a distance scale or a dedication. All this is important information helping you to identify the map and its originality.