Traverses
 Fieldwork In Traversing
 Control By Traversing
 Angular Closure
 Linear Closure
 Adjustment Of Traverses
 Function Of Traverses
 Missing Data
 Bearing And Distance Of
    One Line
 Bearing Of One Line,
    Distance Of Another
 Lengths Or Bearings Of
    Two Lines

The Adjustment of Traverses

The following processes are only valid if the traverse closes within an acceptable tolerance.

It is possible to distribute the misclosure of the traverse throughout the network to compensate for the accumulation of random errors. It is important that the process is understood, because statistically it is based on the assumption that the the misclosure is caused by random error in the distance measurement (angular misclosure having already been eliminated). The process cannot be used to eliminate mistakes, all that happens is that the blunder is distributed throughout the traverse instead of being isolated in one or two lines. This only makes a bad job worse!

There are two procedures commonly used to distribute the misclosure, one based on experience and knowledge of the survey, the other based on the theory that the misclosure is proportional to the distance measured.

The three procedures are:

Intuitive Method
Bowditch Method
Graphical Method

Intuitive Method

The 'intuitive' method is commonly used but difficult to explain. It is based on the Surveyor's understanding of the measurement process, and an acknowledgement that a line measured through dense bush in steep country is likely to have 'more' accumulated random error than a line of similar length measured across flat grassy plains. Also, lines measured in the rain, after a pub lunch or just before quitting for the day may not be measured with the same degree of care as those at other times throughout the day. The Surveyor would perhaps add a few centimetres or so to one of these 'suspect' lines and recompute the misclosure.

Bowditch Method

The Bowditch adjustment assumes that the misclosure of a traverse is proportional to the total length of the perimeter (which when using tapes or chains is a valid assumption). The correction applied to each side is proportional to the length of that side as a ratio of the perimeter, and can be expressed as:

The corrections are then subtracted from the original DE to compute the adjusted DE. For example, consider the same traverse table as before:

The correction to the first DE is given by the formula above, and is as follows:

This correction is then subtracted from the original partial Easting to give the adjusted value. This is performed for all the partial Eastings and northings, with the result of the computation being checked (naturally!).

Graphical Method

Although rarely performed, a graphical traverse adjustment is a good illustration of the principles of the Bowditch adjustment. (A graphical traverse could be done where graphical data only had been obtained, for example when using a plane table.)

The traverse is plotted and the misclosure noted. The perimeter of the traverse is then plotted as a horizontal line to a convenient scale and the misclosure plotted to a larger scale at the end of this line. The amount to shift each point can then be determined by the similar triangles created by joining the starting point with the top of the misclosure, (which is exactly what the Bowditch adjustment does). The direction that each point is moved is the same as the direction of the misclosure vector.