Compass Surveying

Compass surveying is a method of land surveying that uses a compass to measure horizontal angles
in the field. It is a simple and efficient technique often employed for preliminary surveys or in places
where more advanced equipment like total stations or theodolites are not available or needed. This
type of surveying helps to establish the relative positions of objects, landmarks, and boundaries by
measuring angles and then applying mathematical principles to create maps or plans.

Key Features of Compass Surveying

• Primary Tool: The compass is the main instrument used, and it typically consists of a
magnetic needle, a graduated circle, and a pivoting mechanism to measure horizontal
angles.

• Angular Measurements: It measures the angle between two lines of sight, with the primary
focus being the bearing or direction of lines relative to a reference meridian (usually
magnetic north).

• Types of Compasses:

o Prismatic Compass: Has a small prism that allows the user to view the graduation
while holding the compass at eye level. It is commonly used for field surveys.

o Surveyor’s Compass: Typically used in more precise applications, and often includes
a scale for measuring distances.

Instruments Used in Compass Surveying

Compass surveying relies on a few key instruments to measure angles and help surveyors determine
the relative positions of various points on the land. The primary tool is the compass, but several
other instruments are used in conjunction with it to enhance accuracy and efficiency. Below is a list
of the main instruments used in compass surveying:

1. Prismatic Compass

The prismatic compass is the most commonly used instrument in compass surveying, especially for
fieldwork. It consists of a magnetic needle, a graduated circle, and a prism for sighting. It measures
horizontal angles and bearings relative to the magnetic north.

• Components:

o Magnetic Needle: Indicates the direction of the Earth's magnetic field (north).

o Graduated Circle: A circular scale that is used to measure the angle of the line of
sight.

o Prism: Allows the surveyor to read the scale without moving the instrument.

o Sighting Line: A mechanism for aiming at a distant object to measure the bearing.

• Usage:

o Measures horizontal angles and bearings.

 o Used to perform traversing in compass surveying.

2. Surveyor's Compass (or Theodolite Compass)

A surveyor's compass is another instrument used for measuring angles, but it is more precise than a
prismatic compass. It is often used for high-accuracy surveys and can measure both horizontal and
vertical angles.

• Components:

o Magnetic Needle: Indicates magnetic north.

o Graduated Circular Scale: Used to read angles.

o Vernier Scale: Provides finer readings of angles for higher accuracy.

o Sight vanes: For aiming at distant points.

• Usage:

o Measures angles with higher precision.

o Primarily used for boundary surveys, large-scale surveys, and property divisions.

3. Chain or Tape Measure

A chain (or measuring tape) is an essential tool for measuring distances in compass surveying. The
most commonly used chains are Gunter's chain (66 feet long) or modern steel tapes, which measure
distances directly between survey points.

• Components:

o Gunter’s Chain: Consists of 100 links, each 7.92 inches long, totaling 66 feet in
length.

o Steel Tape: A flexible tape used to measure distances with precision.

• Usage:

o Used to measure the linear distance between two points.

o Helps in calculating the perimeter and area during a survey.

4. Ranging Rods (or Surveying Poles)

Ranging rods are used to mark the position of specific points on the ground during a survey. These
poles are brightly colored, typically red and white, and are easy to spot from a distance.

• Components:

o Long Poles: Typically made of wood or metal, marked with color bands.

o Height: Often between 5 and 10 feet, depending on the visibility required.

 • Usage:

o Placed at survey points to help establish the line of sight.

o Used in conjunction with a compass to accurately measure angles between points.

5. Level (or Dumpy Level)

Although not always directly part of compass surveying, a level (or dumpy level) may be used to
ensure that the instrument is perfectly horizontal while taking measurements. Proper leveling of
instruments is crucial for accurate surveying.

• Components:

o Leveling Bubble: Ensures the instrument is perfectly horizontal.

o Crosshairs: To align the line of sight.

• Usage:

o Ensures the instrument is correctly positioned and aligned for accurate angular
measurements.

6. Plumb Bob

A plumb bob is a tool used to ensure the instrument is vertically aligned at the survey station. It
consists of a pointed weight suspended on a string.

• Components:

o Weighted End: Provides a steady vertical reference.

o String: Suspends the weight and helps in alignment.

• Usage:

o Used to check the vertical alignment of the survey instrument to prevent errors in
angle measurements.

7. Tripod Stand

A tripod stand is used to support the compass and other surveying instruments. It provides stability
and ensures the instrument is at the correct height for accurate measurements.

• Components:

o Three Legs: Adjustable for uneven terrain.

o Central Platform: Holds the compass or other instruments.

• Usage:

o Provides a stable platform for instruments to ensure precision.

 o Used to hold the compass steady while the surveyor measures angles.

8. Compass Box (or Surveying Box)

A compass box is a protective carrying case used to store and transport the compass and other
delicate instruments safely.

• Components:

o Wooden or Metal Case: Strong and durable to protect instruments.

o Cushioned Interior: Keeps the compass and related tools safe from damage.

• Usage:

o Protects the compass, chain, and other surveying equipment when not in use.

o Ensures that instruments remain in good condition during transportation.

9. Field Book (or Surveyor's Notebook)

A field book is used to record all measurements and observations made during the survey. This is
where the surveyor notes down angles, distances, and other data.

• Components:

o Paper Sheets: Often ruled, with space for calculations and notes.

o Durable Cover: Protects the book from environmental damage.

• Usage:

o Used to document the details of the compass survey.

o Essential for post-survey data analysis and map creation.

Step-by-Step Procedure of Compass Surveying

Compass surveying is a process that involves measuring horizontal angles between survey stations
and determining distances to map the area or perform a survey. Here's a detailed, step-by-step guide
to compass surveying:

Step 1: Preparing for the Survey

Before starting the survey, you need to ensure that all the required instruments and equipment are
ready. This includes:

• Prismatic Compass (or Surveyor’s Compass)

• Chain or Tape Measure for measuring distances

• Ranging Rods (or Surveying Poles)

 • Level (to ensure the compass is horizontal)

• Plumb Bob (for vertical alignment)

• Field Book to record measurements and observations

• Tripod Stand (to stabilize the compass)

Step 2: Setting Up the Compass

1. Select the First Station: Choose a convenient starting point for the survey, usually a known
location or reference point.

2. Set Up the Compass on the Tripod:

o Place the compass on the tripod stand and level it using the leveling bubble. Ensure
the instrument is horizontal.

3. Align with the North: Use the magnetic needle in the compass to orient the instrument with
the magnetic north. If necessary, correct for magnetic declination if the true north is
required.

4. Position the Plumb Bob: Suspend the plumb bob to ensure the compass is vertically aligned
directly above the station point.

Step 3: Measuring the Angle (Bearing)

1. Sight the First Point: With the compass properly set up, use the sighting vane or prism to aim
the compass at a known point or a point to which the next station is to be set.

2. Record the Bearing: The compass will indicate the bearing (horizontal angle) of the line
between your station and the sighted point. In the fieldbook, record this bearing along with
any necessary information, such as the distance to the next station.

3. Take Multiple Readings (if necessary): If you need to measure angles between multiple
points, use the compass to sight subsequent points, and record each bearing as you go.

Step 4: Setting Up the Second Station

1. Move to the Next Station: After recording the bearing, move to a new point in the direction
indicated by the compass. This station will be the next point for measuring angles.

2. Place the Ranging Rod: At the new station, place a ranging rod or surveying pole to mark
the point clearly.

3. Level the Compass: Again, set up the compass on the tripod at the new station, ensuring it is
properly leveled and aligned with magnetic north.

Step 5: Measuring the Distance

 1. Use the Chain or Tape Measure: Use a chain or measuring tape to measure the straight-line
distance between the two stations.

2. Record the Distance: In the fieldbook, note the distance along with the bearing and other
relevant details.

Step 6: Repeat the Process

1. Move to the Next Station: After completing the measurements for the second station, move
to the next point along the line of the survey. Repeat the process of measuring angles,
setting up the compass, and recording the distance and bearing for each station.

2. Record Bearings for Every New Station: As you continue, always ensure the compass is set
correctly and that bearings between stations are accurately recorded. In most surveys, a
closed traverse (where the last point connects back to the starting point) is often used.

Step 7: Closing the Traverse

1. Close the Traverse: Once you reach the final station, ensure that you return to the starting
point. The bearings and distances recorded should allow you to close the loop by confirming
that the final point matches the initial one. If there is any discrepancy (which is common due
to human error or instrument limitations), adjust accordingly.

2. Check for Errors: If the traverse does not close perfectly, the errors are typically accounted
for in the calculations or by adjusting angles slightly. Ensure all data is carefully checked.

Step 8: Final Calculations

1. Adjust the Bearings: If there was an error in closing the traverse, apply correction methods
such as angle summation to balance the discrepancies.

2. Calculate Distances: Using the recorded distances and angles, calculate the coordinates of
each point on the map.

3. Prepare the Survey Map: Using the data, create a map of the area by plotting the points
based on their coordinates and connecting them to form a layout of the land surveyed.

Step 9: Documentation and Reporting

1. Complete the Field Book: Ensure that all bearings, distances, and any other observations are
fully recorded in the field book.

2. Prepare a Survey Report: Create a final survey report detailing the methods used, the results
of the survey, and the map or layout of the area.

3. Review for Accuracy: Double-check all measurements, calculations, and recorded data to
ensure accuracy before final submission or use.
Conclusion

Compass surveying is a relatively simple but effective method of land surveying, especially for
preliminary surveys or smaller-scale projects. The process involves taking angular measurements at
various points, moving between stations, and recording both distances and bearings. By following
the step-by-step procedure outlined above, a surveyor can map an area, establish boundaries, or
measure features of a landscape.

Advantages of Compass Surveying

Compass surveying offers several benefits that make it a popular choice for certain types of surveys.
Here are the key advantages:

1. Simplicity and Ease of Use

• User-friendly: Compass surveying is relatively simple and easy to learn, making it an

accessible method for beginners and for field surveys that do not require advanced
instruments.

• Minimal Training Required: The basic principles of compass surveying, such as measuring
angles and distances, are straightforward, meaning surveyors can quickly acquire the
necessary skills to perform surveys.

2. Cost-Effective

• Low Equipment Cost: Compared to more advanced instruments like total stations or GPS
systems, the compass and other tools used in compass surveying (e.g., chains or tapes,
ranging rods) are inexpensive.

• Affordable for Small Surveys: This makes it an economical choice for small-scale surveys,
boundary marking, or preliminary work where high precision is not critical.

3. Portability and Convenience

• Lightweight and Easy to Transport: The compass, measuring chain, and other equipment are
relatively light and compact, making them easy to transport over long distances or to remote
areas without specialized vehicles or equipment.

• Suitable for Field Surveys: Since the equipment is portable, it is ideal for surveying in rugged,
remote, or difficult-to-reach areas where carrying heavy or complex equipment would be
impractical.

4. Quick and Efficient

• Fast Setup and Use: Setting up the compass and measuring distances with a chain or tape is
relatively quick, making compass surveying an efficient method for mapping out areas or
determining boundaries in the field.
 • Effective for Preliminary Surveys: Compass surveying is well-suited for quickly gathering
basic data or conducting an initial survey before more detailed methods are used.

5. Minimal Environmental Impact

• Non-Intrusive: Compass surveying typically requires no major modifications to the land or

environment. It is a low-impact method, especially when compared to modern techniques
that may involve more complex setups or excavation.

• Suitable for Sensitive Areas: It is a suitable option for surveying in environmentally sensitive
areas where minimizing disturbance to the landscape is a priority.

6. Effective for Large Areas

• Good for Broad Surveys: Compass surveying is particularly useful for surveying large, open
areas where high precision is not required, such as when determining property boundaries,
mapping general topography, or conducting rough land surveys.

• Wide Coverage: It can cover large tracts of land in a relatively short period of time compared
to more intricate survey methods.

7. Minimal Maintenance

• Low Maintenance of Equipment: The instruments used in compass surveying, particularly

the compass and tape measure, require minimal maintenance compared to advanced
instruments like theodolites or GPS units.

• Durability: The equipment is robust and can be used in various weather conditions, requiring
little more than basic cleaning and occasional calibration.

8. No Need for Advanced Technology

• Independent of Modern Technology: Compass surveying does not rely on electronic devices,
power sources, or advanced software. This can be a significant advantage in remote areas
where access to power is limited or when technology fails.

• Works in Remote Locations: The method is ideal in locations where modern surveying
technologies, like total stations or GPS devices, may not function properly (e.g., in dense
forests, mountainous regions, or areas with poor satellite connectivity).

9. Suitable for Preliminary or Rough Surveys

• Rough Estimations: Compass surveying is effective for rough or preliminary surveys where
high precision is not essential, such as during early planning stages for construction, land
division, or basic topographic studies.
 • Basic Mapping: It provides a reliable way to quickly sketch a general layout of a land area,
which can later be refined with more precise methods if needed.

10. Flexible and Adaptable

• Can Be Used for Various Survey Types: Compass surveying can be applied to a wide range of
survey types, including boundary surveys, topographic surveys, property mapping, and
road alignment surveys.

• Scalability: It can be used for small-scale or large-scale surveys, making it versatile across
different project sizes.

Disadvantages of Compass Surveying

While compass surveying has several advantages, it also comes with a number of limitations and
drawbacks that may make it less suitable for certain types of surveys. Here are the key
disadvantages:

1. Limited Accuracy

• Lower Precision: Compass surveying generally offers lower accuracy compared to modern
surveying techniques like theodolites, total stations, or GPS. Small errors in measurement
can accumulate over long distances or during multiple stations, making it less reliable for
surveys that require high precision.

• Magnetic Interference: The compass is susceptible to magnetic interference from nearby

objects like iron structures, vehicles, and even large metal objects in the environment, which
can distort the accuracy of readings.

2. Dependence on Magnetic North

• Magnetic Declination: Compass surveying relies on magnetic north, which differs from true
north by a certain angle, known as magnetic declination. This declination varies depending
on the geographic location, so the surveyor must account for it when determining true
bearings, especially in regions with significant magnetic variation.

• Inconsistent Readings: Since the compass is influenced by the Earth's magnetic field, its
readings may not always be perfectly consistent, particularly in areas with fluctuating
magnetic fields or during changes in the weather.

3. Limited to Horizontal Angles

• No Vertical Angle Measurements: Compass surveying primarily measures horizontal angles

and cannot directly measure vertical angles or elevations. This makes it unsuitable for
certain types of surveys, such as those requiring detailed topographic or elevation data.
 • No Height Measurement: If height differences or vertical structures are significant in the
survey area (e.g., hilly or mountainous terrain), compass surveying alone will not provide the
necessary vertical data.

4. Subject to Human Error

• Subjective Readings: Compass readings can be influenced by the skill and experience of the
surveyor. Errors can occur in sighting, taking bearings, or recording data, which may affect
the accuracy of the survey.

• Manual Calculations: Because much of the data recording and calculations are done
manually (especially in traditional compass surveying), human mistakes can lead to errors in
the final results.

5. Ineffective for Long Distances

• Accumulation of Errors: Over long distances or when conducting extensive surveys, small
errors in angle measurement can accumulate, leading to significant discrepancies in the final
results. For this reason, compass surveying is not ideal for large-scale surveys where high
accuracy is needed.

• Prone to Misclosure: When performing a traverse survey (looping back to the starting point),
errors can cause the loop to fail to close, resulting in a misclosure, especially when the
survey covers large distances.

6. Limited Use in Urban Areas

• Magnetic Interference in Cities: In urban environments with many large metal structures,
vehicles, and other magnetic sources, compass readings can be highly unreliable due to
interference from local magnetic fields.

• Difficulty in Sighting: In crowded or heavily built-up areas, it may also be difficult to sight
distant landmarks or establish clear lines of sight for accurate angle measurements.

7. Requires Clear Line of Sight

• Obstacles in the Terrain: Compass surveying is highly dependent on having a clear line of
sight between stations. In areas with dense vegetation, mountains, or other obstacles, it may
be difficult or impossible to measure angles accurately between survey points.

• Limited to Open Land: It works best in open, unobstructed terrain, making it less effective
for areas with complex or obstructed landscapes.

8. Not Suitable for Detailed Mapping

 • Basic Surveying: Compass surveying is primarily used for general surveys and basic mapping.
It is not suitable for creating detailed, high-accuracy maps, as it cannot measure elevations,
detailed contours, or features like buildings and roads with great precision.

• Inaccurate for Construction: For tasks like road construction, land development, or building
planning, more precise methods (e.g., total stations or GPS) are generally required to ensure
the measurements meet construction standards.

9. Prone to Error in Curved Terrain

• Inaccurate on Curved Terrain: When surveying areas with curved or irregular shapes,
compass surveying may produce less accurate results due to the difficulty in maintaining
consistent angles and measurements over long distances or uneven surfaces.

10. Weather Sensitivity

• Impact of Weather Conditions: Weather conditions such as strong winds, rain, or extreme
temperatures can affect the compass’ accuracy, making it harder to take reliable readings,
particularly when surveying in open or outdoor environments.

Conclusion

While compass surveying is a simple, cost-effective, and portable method suitable for basic surveys
and general mapping, its limitations—particularly in terms of accuracy, precision, and reliance on
magnetic north—make it less appropriate for detailed, large-scale, or high-precision surveying tasks.
As a result, modern survey methods such as total stations, GPS, or laser scanning are often preferred
when greater accuracy and versatility are required.