Important terms: Arbitrary bearing: The horizontal angle made by the survey line with reference to arbitrary meridian passing through one of the extremities. True Bearing: It is horizontal distance between the true meridian and the survey line measured in a clockwise direction. Azimuth: it is the horizontal angle or direction of a compass bearing. Arbitrary Meridian: Any convenient direction from a survey station to some well defined permanent object is known as arbitrary meridian. This is used for small area survey or to determine the relative directions of small traverse. Grid Meridian: For survey of country, the true meridian passing through the central place is sometimes taken as a reference meridian for the whole country. Such a meridian is known as Grid meridian.