The Hammer-Aitoff equal-area projection, also called the Hammer projection, is a map projection that is a modification of the Lambert azimuthal equal-area projection. It consists of halving the vertical coordinates of the equatorial aspect of one hemisphere and doubling the values of the meridians from the center. Like the Lambert azimuthal equal-area projection, it is equal area, but it is no longer azimuthal. Its inverse is defined using the intermediate variable z congruent sqrt(1 - (1/4 x)^2 - (1/2 y)^2).