One of six map projections devised by M. Eckert for mapping the entire sphere onto the plane in such a way that the poles are represented by straight lines half the length of the equator. Eckert's map projections are usually identified by Roman numerals from I to VI. Numbers I and II are map projections into the interior of a trapezoid; number I is an equidistant map projection; number II is an equal area map projection. Numbers III and IV represent meridians by elliptical arcs (number III is also known as Ortelius's map projection); number IV is an equal area map projection. Numbers V and VI represent meridians by sinusoidal arcs; number VI is an equal area map projection.