NGS Style Manual‎ > ‎- A -‎ > ‎

above, below

Avoid using above to mean north of or more than.

Acceptable:
            above the Arctic Circle
            above zero

Avoid using below to mean south of, less than, or fewer than.

Acceptable:
            below average
            below zero
            below freezing (and other temperatures)
            below the Equator

See also down.