Davenport, Ivey and Associates, Inc.
So how many "Norths" are there? Not all north arrows are created equally! Here are a few "Norths" that are used in surveying:
Magnetic north - North established by the use of a compass. Due to the fact that the Earth's magnetic field is ever changing, magnetic north changes over the course of time.
True north (astronomic north) - True north can be established by observing celestial bodies (normally the sun or the star Polaris). True north remains constant and does not change over time.
Geodetic north - Sometimes incorrectly called true north. Geodetic north passes through the mean poles of the Earth. The Earth slightly wobbles as it rotates on its axis, creating a minuscule difference between true north and geodetic north.
Grid North - Grid north is an established direction based on a map projection. There are two map projections used in the United States, Lambert and Transverse Mercator. Grid north can easily be determined with the use of modern survey grade G.P.S. equipment.
Other "Norths" that surveyors may find or use are; plat north, deed north, record north, assumed north and site north. Most of these are derived from one of the types of north listed above.
Information on Boundary Surveying