Geographic tongue
(benign migratory glossitis) is a common condition that effects about 2% of the population.
There are no special tests necessary for a diagnosis. A health professional will recognize it by its appearance.
The top of the tongue develops irregular smooth red areas surrounded by white, wavy lines. It looks like the outline of a map, hence the common name "geographic tongue". The position of this "map" changes from week to week as areas heal and new areas become raw. It is a wandering rash. The top layer of the tongue does not shed evenly. In some parts it sheds too quickly, in others it sheds too slowly.
The red areas can sometimes become infected with thrush. The red smooth areas are caused by the loss of filiform papilla, leaving a bald area (denuded). Denuded areas may persist for more than a month. The white area is caused by hyperkeratosis.
It is not infectious. There is no treatment. It follows a benign course and may eventually disappear. Spicy foods and acidic foods may make the thin red areas more painful in some cases but they will not make the condition worse. The cause of geographic tongue is unknown. It is believed that stress plays a factor in its development. It is also thought that allergies may be involved. Other causes are local irritation of a small portion of the tongue from tobacco, spicy food, alcohol, or other local irritants. Avoid these if they cause pain.
info gleaned from various sites including these...
http://www.usc.edu/hsc/dental/opath/Chapters/Chapter14_Main.html#GeographicTongue
http://www.nlm.nih.gov/medlineplus/ency/article/001049.htm