Central Meridian: Straight line half as long as the Equator.
Other Meridians: Equally spaced semiellipses concave toward the central meridian. The outer meridians, 180º east and west of the central meridian, are semicircles.
Parallels: Unequally spaced straight parallel lines, perpendicular to the central meridian. Spacing is greatest toward the Equator.
Poles: Lines half as long as the Equator.
Symmetry: About the central meridian or the Equator.
This is an equal-area projection. Scale is true along the 40º30' parallels and is constant along any parallel and between any pair of parallels equidistant from the Equator. It is free of distortion only at the two points where the 40º30' parallels intersect the central meridian. This projection is not conformal or equidistant.
For this projection, only one standard parallel is specified. The other standard parallel is the same latitude with the opposite sign. The standard parallel is by definition fixed at 40º30'.