1.8. Survey Stations

To survey the boundary of an area, the stations taken along the boundary of an area as controlling points are known as survey stations. Figure 1.7 shows the survey stations (P, Q, R and S) marked by black dot enclosed by circle. These stations are definite points on the Earth whose locations have been determined by surveying methods.

Survey stations are specific points established along the boundary of a tract of land. These points are crucial because they serve as reference markers during the surveying process. For example, in Figure 1.7, points labeled P, Q, R, and S are indicated as these survey stations. Their precise locations are determined through various surveying techniques, allowing surveyors to take accurate measurements from these points.

Think of survey stations like the anchor points on a map where you plot your journey. Just as a traveler uses noticeable landmarks to navigate effectively, surveyors rely on these fixed points to accurately measure the land and establish boundaries.

The purpose of survey stations is to provide horizontal control (planimetry, X and Y) and vertical control (Z) during mapping work. In surveying, it is important to know the absolute position of a point/object with respect to a given origin, or its relative position with respect to a known point/object.

Survey stations provide both horizontal and vertical reference points. The horizontal coordinates, expressed as X and Y, allow surveyors to establish a flat representation of the land surface. The vertical coordinate, Z, indicates how high or low a point is relative to a standard level, such as mean sea level. This information is essential for accurately representing the land's features in mapping.

You can think of it like using GPS coordinates on your smartphone. Just as your GPS tells you where you are specifically on earth (latitude, longitude, and elevation), survey stations provide the exact coordinates needed to map and understand land features.

Survey stations are selected by the surveyors at commanding positions in an optimal manner, keeping in view the following criteria: (i) Survey stations should be visible from at least two or more other survey stations. (ii) As far as possible, survey stations must be situated so as to cover minimum elevation and maximum elevation of the area. (iii) The criteria for selecting the survey stations is that lines joining them should not make obtuse angle (>120°) or acute angle (<30°) with each other. (iv) Survey stations should be as few as possible, as more the stations more will be the observational work. (v) Survey stations should be avoided at busy locations as it might affect the smooth measurement of survey observations.

Selecting appropriate locations for survey stations is critical for effective surveying. Firstly, visibility ensures that surveyors can easily see each station from another, enabling accurate alignment and measurements. The second consideration involves elevation; stations should represent variations in height across the area. Thirdly, the angles between the lines connecting the stations need to be avoided from being acute or obtuse to minimize errors. Fewer stations mean less work and more streamlined surveying, while locations should be chosen away from busy areas to avoid disturbances.

Imagine setting up a camera to capture an event. You wouldn't want to place it behind a crowd where it can't see the action. Instead, you'd pick spots where your camera has a clear view of the event without obstructions, similar to how surveyors choose their stations.

The horizontal control is provided by two or more stations on the ground which are precisely fixed in position by distance and direction. It provides the basis for controlling the scale of the surveyed map as well as locating the various topographic features present in the area. The most common methods used to locate a point/feature in the field are by measuring: one angle and the adjacent distance, or two distances, or two angles.

Horizontal control through survey stations ensures the accurate representation of the land's features and scale on the map. By having established distances and markers, surveyors can effectively pinpoint locations either by measuring angles and distances or by knowing specific distances between points. This is crucial for creating detailed and accurate maps.

Consider using triangulation to find your location on a map. If you know the distance to two landmarks, you can create a triangle and pinpoint your location, just like surveyors use angles and distances between their stations to map the area.

Vertical control is provided by the Bench Marks (BMs) in or near the area to be surveyed. It is required to correctly represent elevations on a surveyed map, and is usually established by lines of levels, starting and closing on BMs.

Bench Marks are reference points established to provide a standard for measuring elevation. During surveying, these points help ensure that variations in height are accurately captured, essential for creating topographic maps. By following a level line starting from these marks, surveyors can measure and represent heights accurately.

Think of Bench Marks as the measuring line on a level in construction. Just as a builder uses a level to ensure surfaces are straight and even, surveyors use Bench Marks to keep their elevation measurements consistent and reliable.

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