Does the length of a nautical mile (which, by definition, is based on the curvature of the earth at sea level) change with altitude? In other words, is a nautical mile the same length for an aircraft flying at 30,0000 feet as it is for an ocean liner?

A nautical mile is slightly longer than the standard, or "statute," mile we use in our daily lives, coming in at approximately 1.1508 land miles. However, this isn't just an arbitrary difference. The nautical mile has its roots in the very shape of our planet. Based on Earth's longitude and latitude coordinates, 1 nautical mile corresponds to one minute of latitude. One minute of latitude is about 1.1 miles (1.8 kilometers) and one second of latitude covers about 105 feet (32 meters).

In the English measurement system, there is 1 nautical mile per 1.1508 land miles or 6,076 feet. One nautical mile is a length equal to 1,852 meters, or 1.852 kilometers.

The primary reason for using a different measurement system for marine and aviation navigation relates to the curvature of the Earth. As you embark on long-distance travel, Earth's round shape becomes a factor in accurate measurement. Nautical charts employ latitude and longitude, making it much simpler for mariners, pilots and astronauts to measure distances using nautical miles, offering a more precise representation of the route traveled.

A nautical mile is based on the circumference of planet Earth. If you were to cut Earth in half at the equator, you could pick up one of the halves and look at the equator as a circle. You could divide that circle into 360 degrees. You could then divide a degree into 60 minutes. A minute of arc on the planet Earth is 1 nautical mile. Nautical miles as units of measurement are used by all nations for air and sea travel.

nautical miles are defined as 1,852m wherever you're using it. But I do sort of see what you mean; if you look at the relationship between minutes of latitude and nautical miles, then it's only exact at sea level. However, the difference is tiny. There are around 21,600 nautical miles in the Earth's circumference, and that figure increases by 2? nautical miles for every nautical mile of altitude. To make a 1% difference (216nm) you'd need to fly at around 35 nautical miles; most jet aircraft fly at 4-6nm. Generally you're flying from land, to land. So the difference goes away as you descend anyway.