Geographical And Time Coordinates
---------------------------------

When the output grid type is netCDF, the coordinates will be labeled
"longitude", "latitude", or "time" based on the attributes of the input
data or grid (if any) or on the **-f** or **-R** options. For example,
both **-f0x** **-f1t** and **-R**\ 90w/90e/0t/3t will result in a
longitude/time grid. When the x, y, or z coordinate is time, it will be
stored in the grid as relative time since epoch as specified by
:term:`TIME_UNIT` and :term:`TIME_EPOCH` in the
:doc:`gmt.conf </gmt.conf>` file or on the
command line. In addition, the **unit** attribute of the time variable
will indicate both this unit and epoch.
