Right, I only meant that the metric system is not used. But I'm confused. Are feet and NM not part of the standard Imperial units of measure?
"Imperial units" is ambiguous and can refer to many different sets of units all sharing the same name. US Customary units use SI as a baseline for measuring based on physical constants, and standardized conversions from them to units very similar to what was conventional. Eg, since the meter is defined by the distance light travels in a vacuum for the duration of 1/299,792,458 second, and the US defines an inch to be exactly 2.54 cm, any refinement to the speed of light inherently changes the length of an inch. 12 inches equals a foot, a mile equals 5280 feet (exactly 1609.344 meters), and all these things are based on physical constants. Nautical miles are defined as exactly 1852 meters, which is approximately 1.15 miles.
In addition to the other replies you're getting here, the US for instance does not use imperial units, despite what many people on the internet believe. Imperial units are used by the UK (hence the term "imperial"). The US uses "US customary units", which sometimes overlap with UK units, and other times have the same name but are different. An imperial gallon is quite different from a US gallon, for instance, but imperial and US inches are the same.