Closed loop/link traverse, grid plotting

Closed loop and closed link traverse

• Closed loop traverse: the traverse starts and ends at the same station and forms a polygon. Checks: sum of interior angles $=(2n-4)\times 90^\circ$, and $\Sigma\text{Lat}=0,\ \Sigma\text{Dep}=0$.
• Closed link (connecting) traverse: the traverse starts at one known station and ends at another known station, both with known coordinates, and with known reference bearings at the two ends. Checks: the computed bearing of the last line must equal its known value, and the computed coordinates of the last station must equal the known ones.

Plotting by grid coordinates

1. Choose a scale so that the whole traverse fits on the sheet (for example 1 cm = 10 m). Find the range of N and E values, i.e. maximum minus minimum, and divide by the scale to get the size of sheet needed.
2. Draw the grid of squares (the grid sheet) and label the grid lines with northing (vertical axis) and easting (horizontal axis) values, choosing an origin near the south-west corner so that all plotted values are positive.
3. Convert each station's independent coordinates to plotting units. For example, with scale 1 cm = 10 m, a station at $(N, E)$ is plotted $(E-E_0)/10$ cm along the east axis and $(N-N_0)/10$ cm along the north axis from the origin $(N_0, E_0)$.
4. Mark each station with a fine pencil dot, measuring its position from the nearest grid lines with a scale (no protractor is needed), and circle it with the station name.
5. Join the stations in order with thin lines, and check that each plotted line length, measured with the scale, agrees with the field length. This is a check against blunders.
6. Plot the details (offsets and radiations) from the stations, ink the map and add the title, scale, north arrow, legend and border.

Advantage: each station is located independently by its coordinates, so plotting errors do not accumulate, and the closing check is automatic.