The units in which the length should be computed. Defaults to the unit of the spatial reference system.
The unit name must match the UNIT_NAME column of a row in the ST_UNITS_OF_MEASURE view where UNIT_TYPE is 'LINEAR'.
The ST_Area method computes the area of a surface. The units used to represent the area
are based on the specified linear unit of measure.
For example, if the specified linear unit of measure is feet, the
unit used for area is square feet.
This method can not be used with geometries in round-Earth spatial reference system.