glossary of terms in map history
A map of the observable celestial heavens on the stereographic projection, as per Ptolemy (see Sidoli and Berggren 2007).
With European incursions south of the Equator expanding the observed night sky, some commentators (and accordingly modern historians) distinguished between celestial hemispheres (each showing precisely one hemisphere) and celestial planispheres per se (each showing more than one hemisphere), but many other commentators did not.
By extension, in early modern usage, a terrestrial world map in hemispheres on the stereographic projection.
¶ planisphere (2)
A common, modern term for a world map that has been consciously constructed according to the principles of transformation from a spherical to a flat surface, whose primary purpose is locational. This is a modern term that has been applied retrospectively both to early modern world maps made in the form of sea charts—i.e., world maps that are not schematic mappamundi (Woodward 1987, 287)—and to any world map on a projection (not just the stereographic).