Absolute lowest altitude you can fly (legally)

Gentlemen and Ladies:

Sorry, but if I read these correctly . .

Knots are not dimensionless in aviation. A knot is one nautical
mile per hour, and that nautical mile is the distance corresponding to
one minute of latitude at the equator.

Yes, _if_ someone is navigating by dead reckoning. My point was that
hardly anyone uses dead reckoning by hand these days. And as one
increases in latitude, the 1 degree = 1 minute relationship gets more
and more iffy, too.

It appears to me (unless I misunderstand the posts cited above) that there
may be a misunderstanding of latitude and longitude's relationship to
Nautical Miles.

If I recall correctly, 1 min of latitude = 1 NM everywhere (not just the
equator), aren't lines of latitude also called parallels and thus maintain
there equidistant relationship all the way to the poles? And don't lines of
longitude meet at the poles and therefore their angles maintian the same
angular relationship yet the distances decrease the further one travels from
the equator?

Regards,

Watson