Parent Topic: PROJ
A UPS grid zone can be divided further. However within EASI/PACE, 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.