Stokes parameters are values that describe polarization of electromagnetic radiation. They were developed by George Gabriel Stokes in 1852. Different versions exist, all equivalent to four scalar values that indicate a three-dimensional vector regarding the direction of polarization and a fourth to distinguish between the EMR's intensity and its (fractional) degree of polarization. In one version (Cartesian coordinates), they are called I, Q, U, and V where I is the intensity of the beam and the others indicating the geometry of the polarization. The four are also sometimes labeled S1 through S4 (for I, Q, U, and V). A Stokes map is a map of a portion of the celestial sphere indicating the values over the extent of the map of one or more Stokes parameter.