Contour Definition in Inspection: Understanding the Process

In land surveying, contours are a crucial element in mapping out topographic features of an area. Contours define the shape and elevation of terrain, making them essential for various applications such as construction planning, engineering, and environmental studies. In this article, we will delve into the definition of contour lines, how they are created, and the process of establishing vertical and horizontal controls.

Interpolation and Grid Squares

The process of creating contours begins with interpolation, which involves drawing contour lines between grid points. A grid square is first drawn on a drawing sheet, and then levels of all grid points are established through levelling. The standard square dimension can range from 5 meters by 5 meters to 20 meters by 20 meters.

Reduced Levels and Contouring

In the indirect method of contouring, levels are taken at a few specified spots, and their levels are decreased using this procedure. This method is time-consuming but accurate, making it ideal for projects that require precise topographic information. To speed up the levelling process, hand levels and Abney levels can be used.

Establishing Vertical and Horizontal Controls

Vertical control is established by taking fly levels from a nearby benchmark and setting a level on a commanding location in the area. A levelling instrument is widely used for this purpose. Once vertical control is achieved, horizontal control is set up to determine the position of points on the chosen contour line.

Plane Table Survey and Staff Readings

For large-scale projects, a plane table survey is an excellent choice. This involves establishing multiple points on one or two contour lines and noting them down. The instrument operator then guides the staff operator to another location where they can find the identical staff reading. The required staff reading for a contour line is calculated using instruments, and horizontal control of that location is established.

In conclusion, contour definition in inspection involves interpolation, grid squares, reduced levels, and establishing vertical and horizontal controls. Understanding the process of creating contours is essential for land surveying, construction planning, and environmental studies. By following the steps outlined above, professionals can ensure accurate topographic information that meets project requirements.

Contour definition in inspection