Publication details: New Zealand Government Railways Department, Wellington

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Part of: The Railways Magazine

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# Methods of Procedure

#### Methods of Procedure.

Surveyors use standard blocks when surveying (usually at daylight) in town areas, so as to avoid interruption from street traffic, and have probably been seen doing so by many persons. All surveys are connected by measurement to the nearest trig station in the country, and to a standard block in a town. This permits of any survey being subsequently reproduced with great accuracy from the trig or standard block.

We will assume it is desired to survey an estate for subdivision. The surveyor proceeds to a convenient trig in the vicinity, takes an. observation to an adjacent trig, the bearing and distance of which is recorded on the triangulation maps. Survey lines are then run around the boundaries of the estate, the bearing of each line and its accurate horizontal measurement being recorded, and so back to the starting point at the trig. If the work has been well done the distance travelled north will equal the distance travelled south, and the distance travelled page 15 east will equal the distance travelled west, or at least within the limits of error allowable, which are very small. In Fig. No, 12 is shewn such a survey. The survey is plotted on a plan to scale, the bearings as they deviate from north-south and east-west being calculated. Thus if a line 20 chains long has a bearing of 15 degrees from true north the line has proceeded a certain distance north and also a little to the east. We have a triangle shewn in Fig. 12a, and the northing and easting are computed by the same methods as previously explained for solving the unknown measurements of triangles.

In plotting the plan it is interesting to note that each point north, south, east or west, of the original starting place of the survey at the trig, is plotted in relation to the trig and not in relation to the previous point, as the plotting of the different points proceeds. For instance, a joiner has a piece of moulding 36in. long, which he desires to mark off in inch lengths. If he measured one inch and then another inch, and so on to the end, he would find the last inch short or long, through accumulated errors in the 36 markings. If, however, he measures one inch then two inches, three inches, and so on, all from the one end, each inch marking would be self-contained and have no accumulated error.

The plan having been completed, the subdivision lines are decided upon, and these are reproduced on the ground, using the points of the original survey for check purposes. If it is desired to subdivide a piece of land of unknown area the survey is made and the area is computed from the plan. On the other hand, if it is desired to subdivide a given area the subdivision is computed from the plan and reproduced on the ground.

Surveys are made of all mine workings underground, for it is by this means all material that can be safely removed is brought to the surface. The only method of ascertaining the proximity of adjoining headings and galleries is by accurate survey and plotting on plans.

(To be continued.)