Geographical mile
Encyclopedia
The geographical mile is a unit of length determined by 1 minute of arc
along the Earth
's equator
. For the 1924 International Spheroid this equalled 1855.4 metre
s. Any greater precision depends more on choice of standard than on more careful measurement: the length of the equator
in the World Geodetic System
WGS-84 is 40,075,016.6856 m which makes the geographical mile 1855.3248 m, while the International Astronomical Union
standard IAU-2000 takes the equator
to be 40,075,035.5351 m making the geographical mile 1855.3257 m, almost a millimetre longer.
It was closely related to the nautical mile
, which was originally determined as 1 minute of arc along a great circle
of the Earth, but is nowadays defined as exactly 1852 metres. The US National Institute of Standards and Technology (NIST) notes that: "The international nautical mile of 1 852 meters (6 076.115 49...feet) was adopted effective July 1, 1954, for use in the United States. The value formerly used in the United States was 6 080.20 feet = 1 nautical (geographical or sea) mile." A separate reference also identifies the geographic mile as being identical to these international nautical miles (and slightly shorter than British nautical miles, which were identified as being equivalent to 1853.184 meters). The unit is not used much, but is cited in some United States
laws (e.g., Section 1301(a) of the Submerged Lands Act, which defines state seaward boundaries in terms of geographic miles). While debating what became the Land Ordinance of 1785
, Thomas Jefferson
's committee wanted to divide the public lands in the west into “hundreds of ten geographical miles square, each mile containing 6086 and 4-10ths of a foot” and “sub-divided into lots of one mile square each, or 850 and 4-10ths of an acre”,
The Danish
and German
geographical mile (geografisk mil and geographische Meile or geographische Landmeile, respectively) is 4 minutes of arc, and was defined as approximately 7421.5 metres by the astronomer Ole Rømer of Denmark
. In Norway
and Sweden
, this 4 minute geographical mile was mainly used at sea (sjømil), up to the beginning of the 20th century.
Minute
A minute is a unit of measurement of time or of angle. The minute is a unit of time equal to 1/60th of an hour or 60 seconds. In the UTC time scale, a minute on rare occasions has 59 or 61 seconds; see leap second. The minute is not an SI unit; however, it is accepted for use with SI units...
along the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
's equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
. For the 1924 International Spheroid this equalled 1855.4 metre
Metre
The metre , symbol m, is the base unit of length in the International System of Units . Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole , its definition has been periodically refined to reflect growing knowledge of metrology...
s. Any greater precision depends more on choice of standard than on more careful measurement: the length of the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
in the World Geodetic System
World Geodetic System
The World Geodetic System is a standard for use in cartography, geodesy, and navigation. It comprises a standard coordinate frame for the Earth, a standard spheroidal reference surface for raw altitude data, and a gravitational equipotential surface that defines the nominal sea level.The latest...
WGS-84 is 40,075,016.6856 m which makes the geographical mile 1855.3248 m, while the International Astronomical Union
International Astronomical Union
The International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...
standard IAU-2000 takes the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
to be 40,075,035.5351 m making the geographical mile 1855.3257 m, almost a millimetre longer.
It was closely related to the nautical mile
Nautical mile
The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...
, which was originally determined as 1 minute of arc along a great circle
Great circle
A great circle, also known as a Riemannian circle, of a sphere is the intersection of the sphere and a plane which passes through the center point of the sphere, as opposed to a general circle of a sphere where the plane is not required to pass through the center...
of the Earth, but is nowadays defined as exactly 1852 metres. The US National Institute of Standards and Technology (NIST) notes that: "The international nautical mile of 1 852 meters (6 076.115 49...feet) was adopted effective July 1, 1954, for use in the United States. The value formerly used in the United States was 6 080.20 feet = 1 nautical (geographical or sea) mile." A separate reference also identifies the geographic mile as being identical to these international nautical miles (and slightly shorter than British nautical miles, which were identified as being equivalent to 1853.184 meters). The unit is not used much, but is cited in some United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
laws (e.g., Section 1301(a) of the Submerged Lands Act, which defines state seaward boundaries in terms of geographic miles). While debating what became the Land Ordinance of 1785
Land Ordinance of 1785
The Land Ordinance of 1785 was adopted by the United States Congress on May 20, 1785. Under the Articles of Confederation, Congress did not have the power to raise revenue by direct taxation of the inhabitants of the United States...
, Thomas Jefferson
Thomas Jefferson
Thomas Jefferson was the principal author of the United States Declaration of Independence and the Statute of Virginia for Religious Freedom , the third President of the United States and founder of the University of Virginia...
's committee wanted to divide the public lands in the west into “hundreds of ten geographical miles square, each mile containing 6086 and 4-10ths of a foot” and “sub-divided into lots of one mile square each, or 850 and 4-10ths of an acre”,
The Danish
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
and German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
geographical mile (geografisk mil and geographische Meile or geographische Landmeile, respectively) is 4 minutes of arc, and was defined as approximately 7421.5 metres by the astronomer Ole Rømer of Denmark
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
. In Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
and Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
, this 4 minute geographical mile was mainly used at sea (sjømil), up to the beginning of the 20th century.
See also
- Conversion of unitsConversion of unitsConversion of units is the conversion between different units of measurement for the same quantity, typically through multiplicative conversion factors.- Process :...
- Medieval weights and measures for details of the geographical league of FranceFranceThe French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
- MileMileA mile is a unit of length, most commonly 5,280 feet . The mile of 5,280 feet is sometimes called the statute mile or land mile to distinguish it from the nautical mile...
for the various other miles in use - Nautical mileNautical mileThe nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...