In order to obtain accurate measurements across a wide variety of topographic features, surveyors look to not just one, but four norths, each of which denotes a different direction and point of reference. Many people outside of the profession don’t realize just how flexible the term “north” really is. Rather than referring to just one fixed point on a map, north can refer to a number of different directional headings. In this entry, we’ll take a closer look at the four norths.
True North
Our first north is directed toward the Geographic North Pole, the point at which all the lines of longitude on the Earth intersect in the northern hemisphere. The Geographic North Pole is the North Pole denoted on globes and atlases. Because the Magnetic North Pole is offset from this point, a compass does not point toward true north.
Magnetic North
This north, in contrast to true north, is the direction that compasses point toward. Because the Magnetic North Pole shifts gradually over time due to changes within the Earth’s core, magnetic north does not denote a static heading.
Grid North
As its name suggests, grid north refers to the northern direction on the grid lines of map projections. From its terminus at the Geographic South Pole, grid north follows the direction of the Prime Meridian.
Assumed North
This north is relative to the orientation and reference point of a subject. Let’s say we have an east-west boundary line that runs along the edge of a property. A line directly perpendicular to that boundary is said to be pointed in the direction of “assumed north.” Assumed north measurements are unique to individual surveys, and do not refer to other assumed north measurements from other surveys.
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