Field procedure of compass traversing

A compass traverse is a series of connected lines whose lengths are measured with a chain or tape and whose bearings are measured with a compass. It may be closed (a loop) or open.

Reconnaissance and marking

1. Walk over the area and choose stations so that adjacent stations are intervisible, the lines are free of obstructions, and the stations are away from sources of local attraction (power lines, iron objects).
2. Mark the stations with pegs and fix a ranging rod over each. Draw a reference sketch of each station and an index sketch of the whole traverse.

Observations (at each station)

1. Set up the compass over the station with a plumb bob (or by dropping a pebble) and level it.
2. Sight the ranging rod at the preceding station (back station) and read the back bearing of the previous line; note it.
3. Sight the next (forward) station and read the fore bearing.
4. Measure the length of the line by chain or tape, with offsets and details if required.
5. Move to the next station and repeat. At the last station, close back to the starting station.

Booking

Enter the station names, the lengths, and the FB and BB in a field book. Check that $\text{FB} - \text{BB} = 180^\circ$ for each line.

Checks and closure

• If FB and BB differ by $180^\circ$, there is no local attraction; otherwise, correct the bearings for local attraction.
• For a closed traverse, check that the interior angles sum to $(2n - 4) \times 90^\circ$ and compute the closing error.
• Plot the traverse by the included-angle or coordinate method, and adjust the closing error by Bowditch's rule.