THE CHAIN TRAVERSE

THE CHAIN TRAVERSE.

  An irregular boundary or a winding road or stream may sometimes be traversed by chain alone, although a compass or theodolite traverse is usually preferable in cases where there is no alternative to a traverse of some kind.

                                          

  The method will be understood from fig. 28 and fig. 29, the bends in the lines being fixed by small triangles, of which the lengths of all three sides are measured.

  It will be seen from either of the above examples that a good deal of room is required at the bends in order to get in the extra tie lines or triangles. Hence, the method is not always possible, even when it is otherwise allowable, and the most satisfactory method of survey in such cases is normally an instrumental traverse, either using a compass to measure the directions of the lines, or a theodolite to measure the angles at the bends. The survey of a closed figure like that shown in fig. 29 can be strengthened by one or more tie lines across it, such as the line EC. The method is not sound in practice if any other is available, because the directions of long legs are determined by measurements of triangles with short sides, so that any small linear error in the measurement of the sides of a triangle will be magnified in the swing of the end of the leg whose direction is determined by the triangle.