Most of the contract photography that has been used for mapping, including all the older RAF cover and all Contract cover, is indexed on a series of Record Reference Cover Diagrams at 1:500000 or larger. The written catalogue is a Roneodex card index, with one card per film, recording camera and lens type and number, calibrated principal distance, film type, flying heights, dates of photography, prints held, etc.
A small-scale guide to the main areas of such photography is given by the maps at the back of the DOS Annual Reports from 1951 to 1984.
The principal point of photos used in the mapping are shown and numbered on almost all 1:50000 – 1:125000 topographic maps and provide the most accurate indication of the location of individual photographs.
The Air Photo library contains about 1.5 million black-and-white vertical aerial photographs of survey standard, suitable for viewing stereoscopically in 3D; most photos are at nominal scales of 1:30,000 – 60,000 and in 9” x 9” (230 x 230mm) format. Although mainly panchromatic, there is some infra-red, together with some black-and-white prints off colour or colour infra-red negatives, and a few colour prints.
Nearly all the photography was taken for topographic or land-use mapping purposes, and originates from a variety of sources. Some of the earliest cover held was flown by the USAAF and US Navy over the Caribbean and Pacific islands during the Second World War.
Almost all photography in Africa, southern Yemen, Malaya, and Borneo between 1946 and 1953 was exposed in Fairchild K17 cameras of 6-inch focal length and from 1951 in Williamson F49 cameras with the same focal length. These were carried in RAF photographic reconnaissance aircraft. Throughout the period the planned scale of photography was 1:30000; this was selected as a compromise both to provide specialist departments (e.g. geology, forestry and agriculture) with photography which would permit the interpretation of thematic information and to suit topographic mapping.
Contract photography, flown by British commercial air survey firms using visual navigation methods, was first taken in 1949 and predominates from 1953 onwards. Over 200 contracts were let, each one usually covering the area of a proposed mapping or land use project but, especially in the Caribbean, sometimes extending over several countries and providing cover at several different scales. The scale of photography for 1:50000 mapping since 1954 was usually 1:40000, but from the 1960s, with increasing use of super-wide-angle (3.5-inch focal length) lenses, photography scales are often smaller, 1:50000 or 1:60000. Areas of larger scale mapping were photographed at larger scales; e.g. 1:2500 mapping areas are covered by photography at 1:12500 scale. Areas taken for specialist interpretation purposes may also be at scales larger than 1:40000, 1:25000 being preferred for forestry interpretation, for example.
In addition to contract photography, cover obtained by national survey departments is occasionally held. Later RAF photography, sometimes at very small scales, is held, and also some Royal Navy photography. For many areas, more than one set of cover, of various dates, is available for research into environmental change over the last 40 or 50 years.
Technical records held include camera calibration certificates, film reports with dates and times of photography, and contract documents. The film negatives of RAF and RN photography are usually held by the RAF; those of contract and other cover are held by the national survey department concerned.