Well nautical miles are metric and have nothing to do with fathoms. And metres should have been good, but got buggered by the perverse use of an old Babylonian measurement of angle, the degree, with 90 to the right angle. (360 was a significant number in the Babylonian base 60/base 6 system).

A metre was originally defined in Napoleonic times as 1 ten-millionth of the distance from the equator to the pole (ie 10,000 km from pole to equator). In fact they were ever so slightly out, it's actually about 10,002 km, (or 40,007km around a circumference through the poles). And because the earth isn't perfectly spherical, it's 40,047km around the equator.

It is the bizarre fact of measuring 90 degrees to the right angle that makes the metre a bit annoying, 111.11km to the degree, for navigation purposes. Of course the French tried to make this all work by doing angular measure not in Babylonian degrees but metric grads, also called grades, gradians or gons, which have 100 to the right angle. But sadly they didn't catch on for most purposes. They also put the zero meridian through Paris, but that didn't catch on either.

Nothing imperial about nautical miles. A nautical mile is traditionally 1 minute of latitude. To the nearest metre 1 minute of latitude is 1852m. The nautical mile is today DEFINED as 1852 metres. That's 1012.6859 fathoms. The nautical mile was never 1000 fathoms. The old British Admiralty definition of a nautical mile was 6080 feet, which had the convenience of being precisely 800 feet more than a statute mile, but is clearly not an exact number of yards or fathoms, so it doesn't fit well in the imperial system either. The precise length of a foot varied over time until it was standardised in 1959 (via 1 inch = 25.4mm precisely), and this made the admiralty nautical mile about 1m longer than a modern metric nautical mile.

NASA lost a spacecraft around Mars because someone did some calculations in imperial measurements and got them wrong. I'll stick to metric, thank you.

5m is only about 0.5% different from a rod. So 25m2 is a pretty good equivalent for a square rod, and makes the sums a lot easier.

A hectare is a piece of land 100m by 100m, very easy to visualise. 10,000m2 to the hectare. 100 hectares to the square km, which are those squares on the map, useful for visualising larger areas. Whenever anyone quotes acres to me I immediately convert to hectares or sq km using the 2.5 acres to a hectare approximation.

In much of the continent, it is automatic to describe the floor space of a property in m2. So you can immediately tell what sort of a size property it is. I wish we would do the same.