Geographic tongue is a harmless condition affecting the surface of your tongue. The tongue is normally covered with tiny, pinkish-white bumps known as papillae, which are actually short, fine, hair-like projections. 

With geographic tongue, patches on the surface of the tongue are missing papillae and appear as smooth, red islands often with slightly raised borders.

These patches give the tongue a map-like, or geographic, appearance. The lesions often heal in one area and then move to a different part of your tongue. Geographic tongue is also known as benign migratory glossitis. (Source)