Projection Type
Planar- The Planar mode projects the selected polygons from an orthogonal view determined by the Axis setting. The resulting UV map will actually look quite similar to viewing the model in a 3D viewport set to Top, Front or Side. This mode is very good for quickly assigning areas of a mesh that are all facing the same direction. For more complicated geometry such as a head, Planar will result in a significant amount of UV overlap as the projection will place polygons on both side of the head into the same UV coordinates. Planar Projection would be good for landscapes and some architectural or hard surface models.