Maps Have To Be Accurate,

and as towns, cities, rivers, coastlines and buildings altar over time,

they have to be upgraded, a serious business, but just occasionally a cartographer can fool his or her fellows, by a slipping in a small 'extra' feature, like this marmot or bear shown above, the Swiss Federal Office of Topography (Swisstopo) has employed professional mapmakers for 175 years now, but only now are some of the illustrations being discovered decades after they were embedded in the maps, why would they do this? And how did the hijinks begin? 

from the full article,

'watching a single place evolve over time reveals small histories and granular inconsistencies. Train stations and airports are built, a gunpowder factory disappears for the length of the Cold War. But on certain maps, in Switzerland’s more remote regions, there is also, curiously, a spider, a man’s face, a naked woman, a hiker, a fish, and a marmot. These barely-perceptible apparitions aren’t mistakes, but rather illustrations hidden by the official cartographers at Swisstopo in defiance of their mandate “to reconstitute reality.” Maps published by Swisstopo undergo a rigorous proofreading process, so to find an illicit drawing means that the cartographer has outsmarted his colleagues,'

above on the Swiss border a French nature preserve proudly shows off a fish, for the full article have a look at the hidden pictures in Swiss maps at Eye on Design, I wonder if cartographers to this day are still incorporating their hidden features?