Reconnaissance Survey and Index Sketch in Chain Surveying

Chain surveying undergoes reconnaissance surveys to gather information about the land to be surveyed and the data obtained from this survey is expressed in the form of a key plan called the index sketch. 

Index Sketch

This article explores the basic features and benefits of reconnaissance surveys and index sketches in chain surveying. 

Reconnaissance Survey in Chain Survey

Reconnaissance is defined as the process of primary investigation of the land area to be surveyed. It is called a reconnaissance survey or reconnoiters. In this process, the surveyor walks through the whole area and brings remarks on the following:

1. Obstacles in the area
2. Determine whether the chosen stations are intervisible
3. The stations selected must enclose the whole area
4. Triangles formed are well-conditioned
5. Note the locations of various objects in the area

Also Read: What are well-conditioned and Ill Conditioned Triangles

Index Sketch in Chain Survey

The final report of the reconnaissance survey conducted is brought on a neat hand sketch called as the index sketch or the key plan. It is generally a skeleton plan of the survey work conducted primarily.

An Index sketch shows the:

1. Main Survey Stations
2. Sub-Stations
3. Tie Stations
4. Base Line
5. Arrangement of the framework of the triangles
6. Positions of Objects (Approximate)

An index sketch is an important document held by the surveyor and the one who plots the map. An Index sketch is placed on the first page of the Field Book.

Purpose of Reconnaissance Survey and Index Sketch

A reconnaissance survey and index sketch is an essential component of chain surveying as it provides critical information about the land area to be surveyed. The information gathered during the reconnaissance survey helps in planning the survey work and ensures that the survey is conducted efficiently and accurately. Here are some examples of situations where a reconnaissance survey has helped in the successful completion of survey work:

1. Boundary Survey: Before conducting a boundary survey, a reconnaissance survey helps in identifying the boundary markers, such as fences, walls, or monuments. This information helps in identifying the boundary lines accurately and prevents any encroachment of the neighboring properties.
2. Road Survey: In a road survey, a reconnaissance survey helps in identifying natural and man-made obstacles, such as hills, rivers, and buildings, which may affect the alignment of the road. This information helps in planning the road alignment and ensures that the road is constructed without any hindrance.
3. Pipeline Survey: In a pipeline survey, a reconnaissance survey helps in identifying the natural and man-made obstacles, such as rivers, hills, and buildings, which may affect the pipeline alignment. This information helps in planning the pipeline alignment and ensures that the pipeline is laid without any hindrance.
4. Building Site Survey: In a building site survey, a reconnaissance survey helps in identifying the natural and man-made features of the land area, such as slopes, water bodies, and trees, which may affect the construction of the building. This information helps in planning the construction and ensures that the building is constructed without any hindrance.

Read More On: Construction Surveying