Map users need to understand that there are three different types of north. The three north are the True, the Grid, and Magnetic north. The term Grid north is used in map projection to refer to the direction northwards along the grid lines in the navigation sector. True north (geodetic north) refers to the direction along the surface of the earth as you proceed towards the geographic North Pole. The Magnetic north refers to the direction a compass needle will point corresponding to the magnetic field lines of the Earth.
True north is measured in relation to the geographic North Pole and is generated as the earth rotates on its axis. The direction is marked in our skies by the North Celestial Pole. The direction is within 1° of the placement of Polaris, making the stars trace a trace a small circle in the sky every sidereal day. The True north is seen to rotate in an arc in relation to stars for about 25,000 years to complete. Astronomers estimate that the Polaris will be closest to the Celestial North Pole around the years 2100-02. According to maps from the United States Geological Survey (USGS) and the US Armed Forces, the true north is indicated by a line that ends in a five-pointed star.
Grid north is a navigational phrase used to refer to the northward on a grid lines in a map projection. Grid north contrasts the true north and the magnetic north in that it is aligned to grid lines and always points upwards on a map. According to ordnance survey maps, the grid lines from the grid north sub divides the UK into squares of one kilometer, east of Atlantic Ocean’s imaginary point. The lines point towards the Grid North and have a slight variation from the True North. The variation is slightest along the central meridian of the map and greatest towards the edges of the map. Some navigators ignore the difference between grid north and true north due to their slight difference.
A compass needle will always point towards the Magnetic north pole. The pole may not be the exact point since the compass aligns itself to the local geomagnetic field which varies constantly. The pole is the wandering point in the Northern Hemisphere where the magnetic field points vertically downwards. If a magnetic compass needle is suspended horizontally on an axis it will point straight downwards. The specific point where this occurs is the Geomagnetic North pole. The Position of the North Magnetic pole moves continually northwestward due to adjustments in the magnetic field in the core of the Earth. In the year 2001, the Geological Survey of Canada (GSC) determined that the magnetic north was at the west of Ellesmere Island in Canada. In 2009, the magnetic north was still in Canada within the Arctic Territorial region but was in motion towards Russia at a speed of 55 to 60 kilometers per annum.
The Relationship Between The Norths
The three norths are important to map readers and navigators in making them understand topography. The difference between the magnetic north and the true north is the angle of inclination on a horizontal plane mostly referred to as magnetic variation or declination. Each region has a unique declination and it should be accounted for when reading and analyzing a map. A few degrees can be either added or subtracted to get the specific north one is looking for.