I'm not exactly sure what category to place this discussion. I need some help defining a term. Let's define "North". Here are some terms I hear thrown about: "True North", "Geodetic North", "Due North". What do these terms really mean? I want to be sure I use these terms correctly.

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Subject Tags: Geodesy, Geodetic, North, Plane, Surveying

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The word north is related to the Old High German nord, both descending from the Proto-Indo-European unit ner-, meaning "down" (or "under"). (Presumably a natural primitive description of its concept is "to the left of the rising sun".)

Latin borealis is from Greek boreas "north wind, north", in mythology (according to Ovid) personified as the son of the river-god Strymon, and father of Calais and Zetesseptentrionalis is fromseptentriones, "the seven plow oxen", a name of Ursa Maior. Greek arktikos "northern" is named for the same constellation (c.f. Arctic).

Other languages have sometimes more interesting derivations. For example, in Lezgian kefer can mean both 'disbelief' and 'north', since north of Muslim Lezgians there are areas inhabited by non-Muslim (until recently) Caucasian peoples, such as Avars and Chechens; as well as pagan Turkic peoples. In many languages of Mesoamerica, 'north' also means 'up'.

Magnetic north and declination

Magnetic north is of interest because it is the direction indicated as north on a properly functioning (but uncorrected) magnetic compass. The difference between it and true north is called the magnetic declination (or simply the declination where the context is clear). For many purposes and physical circumstances, the error in direction that results from ignoring the distinction is tolerable; in others a mental or instrument compensation, based on assumed knowledge of the applicable declination, can solve all the problems. But simple generalizations on the subject should be treated as unsound, and as likely to reflect popular misconceptions about terrestrial magnetism.

Maps intended for usage in orienteering by compass will clearly indicate the local declination for easy correction to true north. Maps may also indicate grid north, which is a navigational term referring to the direction northwards along the grid lines of a map projection.

Roles of north as prime direction

The visible rotation of the night sky around the visible celestial pole provides a vivid metaphor of that direction corresponding to up. Thus the choice of the north as corresponding to up in the northern hemisphere, or of south in that role in the southern, is, prior to world-wide communication, anything but an arbitrary one. On the contrary, it is of interest that Chinese and Islamic culture even considered south as the proper top end for maps.

In Western culture:

  • Maps tend to be drawn for viewing with either true north or magnetic north at the top
  • Globes of the earth have the North Pole at the top, or if the Earth's axis is represented as inclined from vertical (normally by the angle it has relative to the axis of the Earth's orbit), in the top half.
  • Maps are usually labelled to indicate which direction on the map corresponds to a direction on the earth,
    • usually with a single arrow oriented to the map's representation of true north,
    • occasionally with a single arrow oriented to the map's representation of magnetic north, or two arrows oriented to true and magnetic north respectively,
    • occasionally with a compass rose, but if so, usually on a map with north at the top and usually with north decorated more prominently than any other compass point.
  • Up is a metaphor for north. The notion that north should always be up and east at the right was established by the Greek astronomer Ptolemy. The historian Daniel Boorstin suggests that perhaps this was because the better-known places in his world were in the northern hemisphere, and on a flat map these were most convenient for study if they were in the upper right-hand corner.

Being the "default" direction on the compass, North is referred to frequently in Western popular culture. Some examples include:

  • The phrase "north of X" is often used to mean "more than X" or "greater than X", i.e. "The world population is north of 6 billion people."

In my opinion, the difference between the three terms are as follows:

  1. True North is simply the direction towards the north pole point. This simply means that in a given survey project, how small it is, there are infinite number of true north direction lines.
  2. Magnetic North is the north direction provided by the compass as it is magnetic in nature. This direction is influenced by the magnetic field in a locality. This also simply means that in a given survey project, how small it is, there are infinite number of magnetic north direction lines.
  3. Grid North is the north direction derived through map projection process. It is a direction used to effect map homogeneity in a flat/2D domain. Grid North direction is contained within specified zone width to minimize distortion.
  4. Geodetic North is an instantaneous north direction of a particular geographic point location. Grid north is parallel to geodetic north direction within same zone. The amount of rotation between true and geodetic north directions at a particular geographic point is termed as convergence angle. This means that in a given project within a single zone, there is only one grid direction line.
  5. Due north is simply a direction towards the adopted north direction line be it arbitrary (assumed or local), magnetic, true, or grid.

Hope this helps.

nice work arnel! i'd go with Arnel's version.....i believe Justin was just trying to help, but Arnel is definitely at the top of his game!  sorry son...nice try

What is "North"?  Almost certainly everybody knows which way is North, or do they?  The answer is that everybody knows what North is and it's relationship with South, East, and West.  The problem is that we all are not coplanar in our reference system.  Does the Sun not rise in the East? Of course. That is the problem with the relative frame of thought when applying direction in a relative way. Is China East or West of the United States?  Well, it is both!  My point is that North only exists in the human mind as a point of reference for a geospatial relationship with other entities exist on Earth.  EARTH!  Which way is North when orbiting the Earth as an astronaut would do?  My guess is that the astronaut would necessarily focus on what is North on Earth, even though he or she is not on Earth.  Imagine that an astronaut ventures so far away that Earth is no longer visible.  Now, which way is North?  Can one be North of the Earth?

Terrestrial reference systems on Earth in a professional sense are commonly called datums.  Within each datum, there are constraining elements that define its parameters as a terrestrial reference system.  North in one datum is not necessarily the same North in another. Although the "Norths" may be generally sharing the polarity of the Earth as a similar point of reference, no datum can be proven to be better oriented than another.  It is all relative to what the information is being used for and at what scale.  The applied value of North as a singularity is worthless out of context.  There is no North unless you call it such.


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