Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In geometry, a hemispherical projection is a mapping from a hemisphere to a disk, used to make a flat picture of the hemisphere. Two main types are used: the equal-angle projection, which is stereographic projection, and the equal-area projection. These projections can be performed by computer, or by hand using special graph paper called a Wulff net or stereonet (for the equal-angle projection) or a Schmidt net (for the equal-area projection). Hemispherical projections are used in structural geology, crystallography, and other disciplines to plot orientations of lines in three-dimensional space. They are also closely related to map projections used in cartography.