Tie or subsi diarylines : A tie line joints two fixed points on the main survey lines. It helps to checking the accuracy of surveying and to locate the interior details. The position of each tie line should be close to some features, such as paths, building etc. Base Lines : It is main and longest line, which passes approximately through the centre of the field. All the other measurements to show the details of the work are taken with respect of this line. Check Line or proof line : It is a line joining the apex of a triangle to some fixed points on any two sides of a triangle. A check line is measured to check the accuracy of the framework.