This projection is actually a combination of two other projections: the Sinusoidal and the Mollweide. The region around the equator is mapped by the Sinusoidal projection, while the mid-latitude to polar regions are mapped with the Mollweide projection. The latitude/longitude values where the switch from one to the other is documented at 44 degrees, 44 minutes, and 12 seconds. In the case of the sinusoidal, the constant, K is always one. Thus, the switch latitude is the latitude at which the Mollweide has a K scale factor of one.