What is Surveying in Civil Engineering?

Surveying is the art of determining the relative positions of points on, above or beneath the surface of the earth by means of direct or indirect measurements of distance, direction and elevation. The process of surveying also includes representations of all results on a sheet of paper known as a plan or map. The application of surveying requires skill as well as the knowledge of mathematics, physics and astronomy to some extent.

Civil surveying is a necessary process in engineering that involves measuring and mapping the details of a land area. These measurements are essential for planning and designing construction projects. The primary goal of surveying in civil engineering is to understand the three-dimensional positions of various points on the land, helping to create accurate plans and layouts for future developments.

Objectives of Surveying in Civil Engineering

The main objectives of surveying in civil engineering are as summarized below:

• To determine the relative position of any objects or points on the earth. 
• To determine the distance and angles between various objects. 
• To prepare a map or plan to represent an area on a horizontal plane.
• To define control points and boundaries of an area, for example, a cadastral survey. 

The fundamental principles of surveying which are the various methods of surveying are based are of two aspects, as follows:

1. Working from whole to part
2. Location of a point by measurement from two points of reference

1. Working from Whole to Part

This principle means that the main framework or control points of a survey must be established first with high precision. Once this strong foundation is in place, smaller and less critical points can be measured with relatively lower accuracy.

For example, a few major control stations are fixed using precise instruments and methods. Then, the rest of the area is surveyed using these as reference points. This approach helps to localise and minimise any errors, so they don’t carry forward or increase as the survey expands. It also ensures that if any mistake occurs in the minor details, it won’t affect the overall accuracy of the survey.

2. Location of a Point by Measurement from Two Known Points

In this principle, the position of a new point is determined by taking measurements from two already known reference points. These known points must be accurately located in the field.

Depending on the situation, angles, distances, or both can be measured to find the unknown point. This technique improves accuracy and avoids relying on a single reference, which could lead to larger errors if that one reference is incorrect. Triangulation, intersection, and resection methods follow this principle.

Classification of Surveying: Plane vs. Geodetic

Surveying is broadly classified into Plane Surveying and Geodetic Surveying, depending on the extent of the area covered and the accuracy required. This classification is essential because the shape of the Earth influences how distances and angles are measured. Understanding the difference helps in choosing the right method for a particular civil engineering project.

Example

• If you're marking out a small residential colony, plane surveying is enough because the curvature of the Earth doesn't affect short distances.

• But if you're involved in mapping a long railway line across several states, geodetic surveying is used because ignoring Earth's curvature could cause significant errors.

This distinction is crucial in civil engineering because using the wrong method can lead to measurement errors that affect the safety and design of the structure.

Surveying Instruments and Their Uses

In traditional surveying, a range of manual instruments are used for measuring distances, angles, and elevations. These tools are easy to use and form the base of many foundational surveying techniques taught in diploma and degree courses.

Modern Surveying Tools

With the advancement of technology, modern surveying has become faster, more accurate, and easier to store digitally. These tools are widely used in large-scale infrastructure projects.