North arrows
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Ordnance SurveyData
OS Data HubNorth arrows are commonplace on maps and are used to communicate the orientation of the map to the user. However, they are not always needed. Indeed, there are certain situations where the inclusion of a North arrow on a map is inaccurate, and this is a common mistake made by novice map makers. (Don’t worry – we’ve all been there). Whether to include a north arrow or not is likely to depend on the scale of the map and its purpose.
A North arrow does what it says, it points North. But which North? There’s True North, Magnetic North and Grid North.
True north, also known as geographic north, is where all the lines of longitude converge at the north pole. Magnetic north, on the other hand, is the direction a compass would point at the time the map is published. Beware though that Magnetic North moves gradually over time and therefore may only be correct at the date of publication. Finally, Grid North is the direction of North on a grid overlaying a flat map, after a projection has been applied (the process of putting the curved surface of the early on a flat piece of paper). Grid North will depend on the projection used and will often differ by a couple of degrees from True North. Most GIS systems will automatically use grid North if you place a north arrow on your map when creating a map layout.
More information about the 3 norths on OS maps can be found here: A Tale of three Norths | OS GetOutside (ordnancesurvey.co.uk)
When choosing which North to use, think carefully about the user of your map. For example, if the user will be navigating using a compass, a written statement or diagram to show how grid north differs from magnetic north might be required. Printed topographic maps often include what is known as a declination diagram which shows the relationship between all three.
On large scale maps, users will generally assume that the top of a map is north unless told otherwise and therefore north arrows can often be omitted from maps where this is true. It is however important to include a north arrow on large scale maps where the orientation of the map is such that north is not at the top. North arrows are also often omitted from thematic maps, where they are not required by the user to understand the subject of a map. Conversely, when knowing the direction of North is critical to the function of the map, such as a map used for navigation or surveying, a north arrow should generally be included. These types of maps may also include a grid to help users to locate and orientate themselves and the map easily.
If you’ve read our section on Projections, you’ll know that the direction of North can vary across a single map due to the projection used (as shown in image below). This variation in the direction of North across a projected map may be negligible at large scales, but at small scales (country to global) can be quite pronounced; for example, on a map of Europe in a Lambert Conformal Conic projection. Placing a north arrow on these small scale maps would therefore be misleading as the direction the north arrow points may only be correct along one line or at one location on your map. In these cases, it may be best to include a graticule which depicts lines of latitude and longitude to help users orientate the map. The variation on North across a map at large scales is negligible and therefore can generally be ignored and a standard north arrow used.
North arrows, despite on many historic maps being quite ornate, should ideally be small, simple and subtle. The north arrow should not visually dominate the map but equally need be large enough that the user can find and use it quickly if required. Similarly, if including a grid or a graticule, these should be visible and usable if required by the user but should not dominate the map image. This can be achieved by keeping line weights fine and colours relatively light.
More recently, creative license has been increasingly used to create stylistic north arrows which embody the theme of a map. These can help to enhance the map’s theme or story it is trying to tell.
More information about the placement of north arrows can be found in our section on map layouts.
