Kōrero: Modern mapping and surveying

Whārangi 3. Aerial photography and maps

Ngā whakaahua me ngā rauemi katoa o tēnei kōrero

Aerial photography

Aerial photography was one of the major developments in the history of modern mapping and surveying. Land that would have taken weeks or months to survey on the ground could be photographed in days, and photographs, once adjusted to remove distortions such as camera angles, could be turned into maps.

The first aerial photograph was taken in New Zealand in 1919, when the chief instructor for the New Zealand Flying School, George Bolt, took the chief photographer of the Auckland Weekly News on a flight over Auckland.

Aerial photography was first used in a survey on 27 March 1926, when the air force did a survey of the Waimakariri River in Canterbury. This covered 160 square miles (414 hectares) and resulted in 67 glass plate negatives. A print of the mosaic created from the photographs still exists.

Photogrammetry

Photogrammetry involves looking at two overlapping aerial images through a stereoscope. This provides a three-dimensional view of the land so an operator can trace contour lines over the image.

In 1931 Bob Crawford, a senior draughtsman with the Department of Lands and Survey, experimented with compiling a map from aerial photographs, using a technique he had read of being used overseas. Based on his experiments, photogrammetry was adopted by the department as a quick and comparatively cheap way of producing topographical maps. A small unit was established in 1936 to undertake aerial mapping.

From 1935, the department imported specialised photogrammetry equipment developed overseas. This allowed an operator to trace the contours of the land and have the tracings mechanically recorded onto paper.

With the adoption of aerial photography and photogrammetry, the work of surveyors in the field was overtaken by that of staff back in the office. In the area of map production, a surveyor’s work was limited to establishing control points for aerial surveys, and checking maps for accuracy.

Topographical maps

Topographical surveys had long been part of surveyors’ work, and the Department of Lands and Survey had first issued topographical maps in 1884. However these were done by manually sketching in the topographic detail, which was time-consuming and could be inaccurate. By the 1930s advances in aerial photography and photogrammetry allowed the department to begin a national series of highly accurate topographical maps.

The first topographical map issued was of Napier and Hastings in 1939. Based on a series of photographs taken by the air force, it was the first map of what eventually became the New Zealand Mapping Service series 1 (NZMS 1), at a scale of 1 inch to 1 mile. Between then and 1945, driven initially by fears of a Japanese invasion, around half of New Zealand was covered with topographical maps, mainly of coastal areas. The final first edition sheet of this map series was published in 1975, although amended editions continued to be issued until 1989.

New Zealand Aerial Mapping Company

It became obvious in the 1930s that the air force would not be able to carry out all the aerial photography required for mapping. The government began to contract out the work, mainly to the New Zealand Aerial Mapping Company, from 1937.

This relationship continued after the Second World War, with the Department of Lands and Survey buying new cameras, lenses and planes and leasing them to the company. By 1962 all of the North Island and two-thirds of the South Island had aerial photography coverage.

Me pēnei te tohu i te whārangi:

Melanie Lovell-Smith, 'Modern mapping and surveying - Aerial photography and maps', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/modern-mapping-and-surveying/page-3 (accessed 13 July 2020)

He kōrero nā Melanie Lovell-Smith, i tāngia i te 24 Nov 2008, updated 17 Aug 2018