PUTTING N.Z. ON THE MAP

Press, Volume C, Issue 29709, 30 December 1961, Page 8

PUTTING N.Z. ON THE MAP

Major Topographical Survey [Specially written for "The Press” by BRIAN CLEMENS] J-JOW many people realise that only seven miles south of, Christchurch lies New Zealand’s highest peak, Mount Cook (12,349 ft); or that Nelson is several miles north of Wellington; and that Dunedin is 180 miles further west than New Plymouth, and 100 miles further west than any point of the North Island. These and many other interesting features of New Zealand geography are relatively little known to the average person. But they are common knowledge to a large band of Lands and Survey Department experts and others who have been engaged in field and office of the biggest mapping project ever undertaken in this country.

Commenced during the war years, the job involves the compiling of inch-to-the-mile maps covering the whole of New Zealand. Work on the mapping has stepped up in recent years, with the help of modern field equipment, and helicopters to transport field parties over alpine country to measure positions and heights which would take weeks to gather by foot. Even so, it will be at least another 10 yean before the whole country is mapped. This is not surprising when it is considered that the task will embrace every inch of New Zealand, including the vastly difficult high alpine areas, and Fiordland in the far south-west, parts of which are still unexplored. The result of the combined efforts of field staff and draughtsmen working to a national programme will be the compilation of detailed topographical maps of the whole 102,000-square-mile land mass of New Zealand. When completed the whole set of maps covering every area of New Zealand would measure about 110 ft long by 15ft wide. The extremely hilly and mountainous nature of our country makes the mapmakers’ task a difficult one. In fiat country maps can be compiled almost directly from aerial photographs. However, in rising country these photographs, unless taken vertically downwards, have a certain amount of “radial distortion” in which peaks and hills appear to be displaced from their true position depending on the height of the feature and its position on the photograph. A minimum number of known "control points” have to be obtained to overcome this problem. From the photographs, drawings are compiled, with the scale brought down to fit the control points. A modern machine now used by the

Lands and Survey Department in this phase of the map-making is a photogrammetric machine which brings the photograph image to the required scale of the chart, correcting for height distortion, and enabling contours to be drawn. In settled areas the control points may be a prominent hill, building, or trig point, the positions of Which are known. However, moot control points in the vast areas of back country have to be provided by field parties, who introduce a triangulation system to determine relative bearings and positions of the surrounding country. A modern aid which has speeded up their work is a tellurometer, a piece of equipment in two parts, one of which sends out a short-wave signal and this is picked up, reflected, and returned by the other part. The machine converts time taken for the signals to travel across intervening country, into distances. Helicopters are being used to an increasing extent by the survey parties, and the field work has been speeded up to an unbelievable extent where these versatile machines have been employed. By “leap-frogging” the control points across high country regions the survey parties have been able to cover in a few days areas which would take several weeks to survey by foot. The material gained by the field parties is passed on to Lands and Survey Department computers, and positions and heights of the selected features used as control points are compiled for the map making. The photogrammetric department then takes over the task, and with the aid of the newly-developed machines, produces a map to the scale fitted to the control points. From these master sheets.

which embody all details of the country, including contours, the map draughtsmen, or cartographers, produce the final drawings, one sheet for every colour to be printed in the finished map. After this stage the maps are ready for final printing. There has been an everincreasing demand for the inch to the mile topographical maps in recent years. Not only are they widely used by sportsmen and tourists but also by catchment boards and soil conservation - councils, and the' Forestry and other Government departments. The Lands and Survey Department itself finds the maps essential in its administration of the large high-country sheep stations which it leases. The chief draughtsman of the Department in Christchurch (Mr C. Holdsworth) said the department began in 1940 amassing aerial photographs of the country for the mapping project. Because of the urgency of mapping the land during the war, many of the early sheets were compiled without aerial photographs, and these will be redrawn in time, adding considerably to the task. As well as the main work of covering the large, difficult areas which were previously unmapped, the project includes revision, with the aid of aerial photographs, of maps which were compiled without photographs, and the revision of maps covering cities, towns and other densely settled areas which are constantly changing. For the latter reason particularly the map makers' job can never be really completed.

An Enormous Task Before the war there were no properly surveyed topographical maps of New Zealand, so that the job undertaken by the department is an enormous one. With more than half the country now covered the department expects to have the work nearing completion iri 10 years. Hie most difficult parts have still to be covered, however, in the ranges of Canterbury, Westland, Otago, and Southland. All New Zealand's peaks above 10,000 ft

are in Canterbury and Westland, and the mapping of such massive high country presents a big problem because of the increased radial distortion. This is due to the height of the terrain in relation to the flying height of the aeroplane taking the photographs. The Fiordland region will be even more difficult by virtue of its steepness, dense bush, and wet, foggy weather, all particularly hazardous to the field parties.

Weather conditions, restricted daylight, and heavy snow over-rule any field work in the high country in the winter. All the work in the mountains has to be carried out in an intensive programme during the summer, and from the material gathered the map makers, working in offices throughout the country, take over the task of putting New Zealand on the map.