1. True meridian- the line on a plane passing through the geographical North Pole or geographical South Pole and any point on the surface of the earth is known as true meridian. It is also called as geographical meridian.
The angle between true meridian and line is known as true bearing of the line. It is also known as azimuth.
2. Magnetic meridian – when magnetic needle is suspended freely and balance properly , unaffected by magnetic substance it indicate a direction this direction is known as magnetic meridian. The angle between magnetic meridian and line is known as magnetic bearing of the line.
3. Arbitrary meridian – sometime survey of a small area a convenient direction is assume as a meridian known as Arbitrary meridian.
The angle between Arbitrary meridian and line is known as Arbitrary meridian of the line.