NAUTICAL MILE

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A nautical mile is a measure of distance. One nautical mile is equal to:

• 1.852 Kilometers
• 1.15078 Miles
• One Minute of Latitude at Any Meridian line

The unit of measurement known as the nautical mile is used by modern mariners, aviators, and anyone else who wants to use a chart or map friendly unit that has international recognition.

First defined at the 1929 inaugural meeting of the International Extraordinary Hydrographic Conference in Monaco, the distance was set at exactly 1,852 meters.

It was not immediately accepted by the entire international community but it is now recognized globally and listed by the International Bureau of Weights and Measures.

Evolution of the Nautical Mile

Without chart navigation it would not be possible to have the nautical mile as we know it today.

Modern charts and maps share many things with early maps of the earth including the lines oflatitude and longitude.

A further division of these sections of a chart yields minutes and eventually seconds.

The lines of latitude which run from the North Pole to the South Pole are equally divided intominutes of arc. Each of these minutes of arc is equal to 1,852 meters.

This is how an equal division of the earth’s natural dimension became known as the nautical mile. The modern measurement of this historical unit gives us the equivalent in meters.

Using Nautical Miles

Because nautical miles are based on the lines of latitude it makes them a natural choice to use on nautical charts. Nautical charts use what is known as the Mercator Projection which draws the globe on a cylinder rather than the familiar sphere. This gives a nautical chart an even grid which doesn't distort at the poles.

When navigating by chart the navigator uses dividers to quickly count of units of distance. To set your divider to one nautical mile simply set it to the same distance of one minute of arc on any chart of any scale.

Some people ask why anyone would still learn chart navigation when GPS is available. There are two answers; instruments break or may be damaged in an accident, and chart navigation skills must be demonstrated to obtain almost any professional maritime license.

Abbreviations of nautical mile are NM, nmi, and less frequently just M.