UPS

In the UPS (Universal Polar Stereographic) grid system, which is used instead of UTM in the polar areas, each circular polar zone is divided in half by the the Prime Meridian (0 degrees Longitude) and 180 degrees Longitude (East or West). There are two grid zones over the North Pole (Y and Z) and two over the South Pole (A and B).

A UPS grid zone can be divided further. However for PCI software the grid zone is only used to determine if the coordinates are at the North or South Pole.

 UPS Grid Zone    Longitude Range    Latitude Range

      A             180W -   0W        90S - 80S
      B               0E - 180E        90S - 80S

      Y             180W -   0W        84N - 90N
      Z               0E - 180E        84N - 90N

 Note: - Grid zones C to X (but not I or O) exist, but are not valid
         for the UPS projection.  They are supported for the UTM
         projection.