norths

outdoors home > navigation > navigation with compasses & other aids

**Grid north and magnetic north are different.** It is crucial for everyone who uses a map and compass to be aware of this and to understand how their navigation techniques must take this into account.

There is more than one "north": 1) True north - obtained from readings from sun and stars (this is sometimes referred to as astronomical true north) 2) True north - marking the north end of the axis of the earth's rotation (geodetic north). This is very close to (1). 3) Grid north - the direction of north shown on a map. Map (or grid) bearings are taken in relation to this north. (It is worth pointing out the different mapping systems use different "grid norths" - this emphasises the need to always check when using a map from a system/country you are not familiar with) 4) Magnetic north - the direction to which the north needle of a compass points. Magnetic bearings are taken in relation to this north. The "magnetic north pole" is moving; because of this the relationship between grid north and magnetic north varies with time.
 * We are interested in grid north (north on our maps) and magnetic north (north on our compasses). **

The size of the difference between magnetic north and the other ones varies between places and over time (OS maps show this information in the margin). The difference between magnetic north and grid north is the "grid magnetic angle" - **if you plan to use a map and compass you MUST know both the magnitude (i.e. how many degrees) and the direction (i.e. is grid north west or east of magnetic north) of the GMA. ** This information is usually found in the margin of the map.

magnetic declination is not the same as the GMA - see this useful [|post] magnetic declination, inclination and deviation explained

In the UK, for the next few years at least, **magnetic north is west of grid north**: to convert between grid and mag bearings: Grid to mag, add <span style="font-family: Georgia,serif; font-size: 19.2px;">Mag to grid, get rid

<span style="font-family: Georgia,serif;">In most of the UK at present (2013) the GMA is approximately 1 to 2 degrees. This means that grid north (which is east of magnetic north) is at a //magnetic (or compass)// bearing of 002. In other words if the grid bearing is x degrees, the magnetic bearing that should be followed on the ground is x + 2 degrees ( <span style="color: #ff0300; font-family: Georgia,serif;">grid to mag, add <span style="font-family: Georgia,serif;">).

<span style="font-family: Georgia,serif;">[|site that shows declination whereever you are] <span style="font-family: Georgia,serif;">[|GMA calculator] (UK only)