Contouring in surveying is the process of determining the elevation of various points on the land and fixing these points of the same horizontal positions in the contour map. It is the science of representing the vertical dimension of the terrain on a two-dimensional map. Contouring is carried out to identify any noticeable difference in elevation of the existing land and to provide a complete and clear image of the land and the surrounding area. The main objective of conducting contour surveys is to understand the topography of the land and to exercise vertical and horizontal control. The following are the methods of contouring:

• Direct method: This method consists of finding vertical and horizontal controls of the points that lie on the selected contour line. For vertical control, a leveling instrument is commonly used. A level is set on a commanding position in the area after taking fly levels from the nearby benchmark. The plane of collimation/height of the instrument is found, and the required staff reading for a contour line is calculated. Horizontal control is established by chain survey, compass survey, or plane table survey.

• Indirect method: In this method, levels are taken at some selected points, and their levels are reduced. Horizontal control is established first, and then the levels of those points are found. After tracing the points on the plan, reduced levels are marked, and contour lines are interpolated between the selected points.

Contour maps are very useful since they provide valuable information about the land. They are used in the starting of any engineering project such as a road, a railway, a canal, a dam, a building, etc. . Contouring is also an essential tool in construction projects to understand the structure of the site, calculate how much soil and other material needs to be added or removed to make the structure of the site fit the construction plan, and to understand and verify how the terraforming of the land fits with the engineering design. To read a contour survey, one needs to understand that contour lines join points at the same elevation, and the closer together the contour lines are, the steeper the section. The further apart the lines are, the shallower the rise or fall of the terrain.