It is unknown whether or not the map is a real 15th century map or a forgery.
The Tartar RelationThe map was discovered bound in the pages of a small book called The Tartar Relation. The book dates back to 1440 and is known to be authentic. It is a description of the history and manners of the Mongols put together by Giovanni Da Pian Del Carpini, a Franciscan friar.
History of the Vinland MapThe Vinland Map first appeared in the early 1960s with its authenticity backed by Yale University, which is the custodian of the map. The authenticity of the map was first questioned in 1966 when the Smithsonian Institution recommended that the map be studied scientifically to determine if it was genuine.
In 1974, the ink on the map was tested and it was found to contain trace amounts of anatase (titanium dioxide), particles that, according to Walter C. McCrone and Lucy B. McCrone of the McCrone Research Institute, did not appear in ink until 1920, do not occur in nature, and could not have been manufactured in medieval times.
In 1976, however, Jacqueline Olin of Smithsonian's Conservation Analytical Laboratory released a study that seemed to contradict McCrone's findings. It found that anatase can, in fact, be a by-product of the medieval process of making oak-gall ink. (More information regarding studies of the anatase can be found here.).
Arguments went back and forth for the next few decades, until 2002, when the parchment was carbon-dated. The carbon dating found that the parchment was near the same age as The Tartar Relation, dating to about 1430. Questions were then raised as to whether the map was indeed genuine or if it was a forgery drawn on a blank piece of parchment taken out of The Tartar Relation.
Another study was also done in 2002 by Katherine L. Brown and Robin J.H. Clark of University College London which confirmed the presence of significant anatase at selected points on the map.