True Meridian vs Arbitrary Meridian
A great circle, which passes through the true north and true south is known as meridian. A circle described by the intersection of the surface of the earth with the plane passing through the centre of the earth is known as great circle. That is, great circle is a circle traced on the surface of a sphere (earth is considered as a sphere) such that both have the same diameter. The 0 degree meridian is known as the prime meridian, from which other meridians or lines of longitude are measured, that passes through Greenwich England. The direction given by the acute angle between a line and a meridian is known as bearing.
True Meridian
The direction from any point along a meridian towards the North Pole of the earth is defined as true north. That is the north according to the earth’s axis. True north is also known as geographic north. True south is also defined in a similar manner. True meridian is defined as the plane that passes through the true north pole and true south pole at the place of observation. True meridian can be established by astronomical observation as it passes through the true north and south. True bearing is the horizontal angle between the true meridian and a line.
Arbitrary Meridian
Arbitrary meridian is any convenient direction towards a well defined permanent object. These meridians are used to determine the relative directions of other lines in a small area. The horizontal angle between a line and the arbitrary meridian is defined as arbitrary bearing. The arbitrary meridian fully ignores the prime meridian.
What is the difference between True Meridian and Arbitrary Meridian? ¤ True meridians are fixed, whereas arbitrary meridians vary with time and location. ¤ True meridian may be established by astronomical observation, while arbitrary meridians are formed by human for their convenience. ¤ True meridian passes through the center of north and south poles, but arbitrary meridians not necessarily pass through true north and south. ¤ Generally, arbitrary meridian is used to determine relative directions, whereas true meridian is used to determine absolute directions. ¤ Arbitrary meridian is suitable for surveying a small area, whereas true meridian can be used to survey large areas.

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