In order to begin excavation of trenches required for a building's foundation, the builder must know the positions and levels of building lines shown on the construction plans on the ground.
That is, the exact length, width, depth, and position of the foundation trenches must be marked on the ground.
This movement from the construction plan to the actual site by transferring dimensions from the layout plan to the ground is called setting out. It is probably the most critical step in the entire construction process.
Various techniques and instruments are used for this process of setting out.