According to Esri, the Robinson "central meridian is a straight line 0.51 times the length of the Equator. Parallels are equally spaced straight lines between 38° N and S; spacing decreases beyond these limits. The poles are 0.53 times the length of the Equator. The projection is based upon tabular coordinates instead of mathematical formulas" (Environmental Systems Research Institute, 1997).
Neither conformal nor equal-area
Meridians are equally spaced, and concave toward the central meridian, and look like elliptical arcs (Environmental Systems Research Institute, 1997).
Parallels are equally spaced straight lines between 38° N and S.
Central meridian and all parallels are linear.
Scale is true along latitudes 38° N and S. Scale is constant along any specific latitude, and for the latitude of opposite sign.
Thematic and common world maps.
This projection has been used both by Rand McNally and the National Geographic Society.
Source: Snyder and Voxland, 1989