This page documents an OPTIMADE Unit Definition. See https://schemas.optimade.org/ for more information.

**ID: https://schemas.optimade.org/defs/v1.2/units/si/general/nauticalmile**

`nauticalmile`

**Unit name:** nautical mile

**Latin symbol:** M

**Display symbol:** M

**Description:** A unit of length primarily used in navigation defined as 1852 m using the current, or one of the historical, definitions of the SI units.

The nautical mile unit appears in the International System of Units (SI), 1st ed. (1970) defined as "1 nautical mile = 1852 m" with the footnote "The nautical mile is a special unit employed for marine and aerial navigation to express distance. The conventional value given above was adopted by the First International Extraordinary Hydrographic Conference, Monaco, 1929, under the name 'International nautical mile'." Historically, the nautical mile was defined as the meridian arc length corresponding to one arcminute of latitude.

- The International System of Units (SI), 1st ed. (1970) categorizes the unit as "Units in use temporarily with the International System."
- The International System of Units (SI), 7th ed. (1998) changes the categorization to "Other non-SI units currently accepted for use with the International System" and adds to the footnote that: "As yet there is no internationally agreed symbol. This unit was originally chosen because one nautical mile on the surface of the Earth subtends approximately one minute of angle at the centre."
- The International System of Units (SI), 8th ed. (2006) changes the categorization to "Other non-SI units" and adjusts the footnote to say: "As yet there is no internationally agreed symbol, but the symbols M, NM, Nm, and nmi are all used; in the table the symbol M is used. The unit was originally chosen, and continues to be used, because one nautical mile on the surface of the Earth subtends approximately one minute of angle at the centre of the Earth, which is convenient when latitude and longitude are measured in degrees and minutes of angle."
- The nautical mile is omitted in the International System of Units (SI), 9th Edition (2019).

The nautical mile unit was implicitly redefined via the redefinition of the metre at the 17th CGPM meeting (1983), resolution 1.

This is a generalized definition taken to reference the current, or one of the historical, SI unit definitions. This definition is intended for situations when it is not possible to be more precise, e.g., in contexts where data have been collected that uses different historical SI definitions.

**Resources:**

- Definition in the International System of Units (SI), 1st Edition
- Redefinition of the metre at the 17th CGPM meeting (1983), resolution 1
- Wikipedia article describing the unit

**Compatibility:** (other definitions that are covered by the above definition)

`https://schemas.optimade.org/defs/v1.2/units/si/1970/temporary/nauticalmile`

`https://schemas.optimade.org/defs/v1.2/units/si/1983/temporary/nauticalmile`

**JSON definition:**

```
{
"$id": "https://schemas.optimade.org/defs/v1.2/units/si/general/nauticalmile",
"$schema": "https://schemas.optimade.org/meta/v1.2/optimade/physical_unit_definition.json",
"title": "nautical mile",
"symbol": "M",
"display-symbol": "M",
"alternate-symbols": [
"NM",
"Nm",
"nmi"
],
"description": "A unit of length primarily used in navigation defined as 1852 m using the current, or one of the historical, definitions of the SI units.\n\nThe nautical mile unit appears in the International System of Units (SI), 1st ed. (1970) defined as \"1 nautical mile = 1852 m\" with the footnote \"The nautical mile is a special unit employed for marine and aerial navigation to express distance. The conventional value given above was adopted by the First International Extraordinary Hydrographic Conference, Monaco, 1929, under the name 'International nautical mile'.\"\nHistorically, the nautical mile was defined as the meridian arc length corresponding to one arcminute of latitude.\n\n- The International System of Units (SI), 1st ed. (1970) categorizes the unit as \"Units in use temporarily with the International System.\"\n- The International System of Units (SI), 7th ed. (1998) changes the categorization to \"Other non-SI units currently accepted for use with the International System\" and adds to the footnote that: \"As yet there is no internationally agreed symbol. This unit was originally chosen because one nautical mile on the surface of the Earth subtends approximately one minute of angle at the centre.\"\n- The International System of Units (SI), 8th ed. (2006) changes the categorization to \"Other non-SI units\" and adjusts the footnote to say: \"As yet there is no internationally agreed symbol, but the symbols M, NM, Nm, and nmi are all used; in the table the symbol M is used. The unit was originally chosen, and continues to be used, because one nautical mile on the surface of the Earth subtends approximately one minute of angle at the centre of the Earth, which is convenient when latitude and longitude are measured in degrees and minutes of angle.\"\n- The nautical mile is omitted in the International System of Units (SI), 9th Edition (2019).\n\nThe nautical mile unit was implicitly redefined via the redefinition of the metre at the 17th CGPM meeting (1983), resolution 1.\n\nThis is a generalized definition taken to reference the current, or one of the historical, SI unit definitions.\nThis definition is intended for situations when it is not possible to be more precise, e.g., in contexts where data have been collected that uses different historical SI definitions.",
"compatibility": [
"https://schemas.optimade.org/defs/v1.2/units/si/1970/temporary/nauticalmile",
"https://schemas.optimade.org/defs/v1.2/units/si/1983/temporary/nauticalmile"
],
"resources": [
{
"relation": "Definition in the International System of Units (SI), 1st Edition",
"resource-id": "https://www.bipm.org/en/publications/si-brochure"
},
{
"relation": "Redefinition of the metre at the 17th CGPM meeting (1983), resolution 1",
"resource-id": "https://www.bipm.org/en/committees/cg/cgpm/17-1983/resolution-1"
},
{
"relation": "Wikipedia article describing the unit",
"resource-id": "https://en.wikipedia.org/wiki/Nautical_mile"
}
],
"defining-relation": {
"base-units": [
{
"symbol": "m",
"id": "https://schemas.optimade.org/defs/v1.2/units/si/general/metre"
}
],
"base-units-expression": "m",
"scale": {
"numerator": 1852
}
},
"x-optimade-definition": {
"label": "nauticalmile_si_general",
"kind": "unit",
"format": "1.2",
"version": "1.2.0",
"name": "nauticalmile"
}
}
```